Full Text

Turn on search term navigation

Published for SISSA by Springer

Received: July 29, 2013

Accepted: September 12, 2013

Published: October 10, 2013

Gauthier Durieuxa and Christopher Smithb

aCentre for Cosmology, Particle Physics and Phenomenology (CP3), Universit catholique de Louvain,Chemin du Cyclotron 2, B-1348 Louvain-la-Neuve, Belgium

bLPSC, Universit Joseph Fourier Grenoble 1, CNRS/IN2P3 UMR5821, Institut Polytechnique de Grenoble,53 rue des Martyrs, 38026 Grenoble Cedex, France

E-mail: mailto:[email protected]

Web End [email protected] , mailto:[email protected]

Web End [email protected]

Abstract: Baryonic R-parity violation could explain why low-scale supersymmetry has not yet been discovered at colliders: sparticles would be hidden in the intense hadronic activity. However, if the known avor structures are any guide, the largest baryon number violating couplings are those involving the top/stop, so a copious production of same-sign top-quark pairs is in principle possible. Such a signal, with its low irreducible background and e cient identication through same-sign dileptons, provides us with tell-tale signs of baryon number violating supersymmetry. Interestingly, this statement is mostly independent of the details of the supersymmetric mass spectrum. So, in this paper, after analyzing the sparticle decay chains and lifetimes, we formulate a simplied benchmark strategy that covers most supersymmetric scenarios. We then use this information to interpret the same-sign dilepton searches of CMS, draw approximate bounds on the gluino and squark masses, and extrapolate the reach of the future 14 TeV runs.

Keywords: Supersymmetric Standard Model, Global Symmetries

ArXiv ePrint: 1307.1355

Open Access doi:http://dx.doi.org/10.1007/JHEP10(2013)068

Web End =10.1007/JHEP10(2013)068

The same-sign top signature of R-parity violation

JHEP10(2013)068

Contents

1 Introduction 11.1 Theoretical framework 21.2 Search strategy at colliders 3

2 Characteristic signatures of the R-parity violating MSSM 4

3 Sparticle decay chains and lifetimes 73.1 Gluino lighter than squarks 73.2 Squarks lighter than the gluino 83.3 Combining sparticle production mechanisms with decay chains 11

4 Simplied mass spectrum and analysis strategy 13

5 Same-sign dileptons at the LHC 165.1 Experimental backgrounds 175.2 Selection criteria 175.3 Current constraints and prospects 185.4 Charge asymmetries 21

6 Conclusion 23

A Decay widths 25A.1 Two-body squark decays 25A.2 Three-body gaugino decays 26A.3 Four-body squark decays 29

1 Introduction

After two years of operation, the LHC experiments have not found any signal of low-scale supersymmetry. Current mass bounds on simple supersymmetric scenarios are now pushed beyond the TeV. This is especially striking in the simplied setting where squarks, gluino, and neutralinos are the lightest supersymmetric degrees of freedom. With the gluino and all the squarks degenerate in mass, the bounds are above 1.5 TeV [1, 2].

Most searches for supersymmetry are done assuming R parity is exact, thereby forbidding all baryon number violating (BNV) and lepton number violating (LNV) couplings [3]. Indeed, at rst sight, the incredibly tight limits on the proton decay lifetime [4] seem to lead to an unacceptable ne-tuning of these couplings. But, imposing R parity is not innocuous for the phenomenology of the Minimal Supersymmetric Standard Model (MSSM). Most dramatically, superpartners have to be produced in pairs and the lightest supersymmetric

JHEP10(2013)068

particle (LSP) is absolutely stable. It thus contributes to the dark matter density of the Universe, and has to be electrically neutral and colorless. So, at colliders, all superpartners cascade decay down to this LSP, which manifests itself as missing energy. In particular, the tight bounds on the gluino and the squark masses are derived looking for the signatures of such cascade decays down to the invisible LSP.

The hypothesis of an exact R parity is thus entwined within current search strategies. This predicament mostly remains even though the original motivation for R parity no longer holds. As was shown in ref. [5, 6], the BNV and LNV couplings do not require any ne tuning to comply with the proton decay bounds. Rather, being avored couplings, they just need to be aligned with the avor structures already present in the Standard Model (SM). In this way, the strong hierarchies of the known fermion masses and mixings, e.g. m mu mt, are passed on to the R-parity violating (RPV) couplings. Conse

quently, low-energy observables, mainly sensitive to the very suppressed rst-generation RPV couplings, naturally comply with all existing bounds.

1.1 Theoretical framework

To precisely dene and enforce the alignment of the RPV couplings with the SM avor structures, the Minimal Flavor Violation (MFV) framework is ideally suited [7, 8]. This is the approach proposed in ref. [5, 6], of which we only sketch the main line of arguments here. The starting point of the MFV hypothesis is the assumption that, at least in a rst approximation, the Yukawa couplings Yu, Yd, and Ye are the only explicit breaking terms (or spurions) of the SU(3)5 avor symmetry exhibited by the MSSM gauge interactions. Then, all the other avor couplings, including those violating R parity, are constructed out of these spurions in a manifestly SU(3)5 invariant way. The main result of this analysis is that the transformation properties of the Yukawa couplings under SU(3)5 allow only for the BNV couplings,

WRPV = IJKUIDJDK , (1.1)

where I, J, K are avor indices. Specically, MFV leads to expressions like

IJK =LMNYILuYJMdYKNd LJK

JHEP10(2013)068

KN . . . ,(1.2)

where serves as a reminder that arbitrary order one coe cients are understood for

each term. By contrast, none of the LNV couplings can be constructed out of the leptonic Yukawa coupling Ye. Even introducing a neutrino Dirac mass term does not help. Actually, it is only once a left-handed neutrino Majorana mass term is included in the spurion list that such couplings can be constructed, but they are then so tiny that they are completely irrelevant for collider phenomenology.

Obviously, once this alignment hypothesis is enforced, the couplings are highly hierarchical. However, the predicted hierarchy depends on additional parameters or assumptions besides MFV itself. First, they strongly depend on tan = vu/vd, the ratio of the vacuum expectation values of the two MSSM neutral Higgs bosons, since Yd Yu when tan [lessorsimilar] 5 (see table 1). Then, specic models might not generate all the possible

IL IMN

YuYd

YdYu

IJK Full MFV Holomorphic MFV ds sb db ds sb db

tan = 5

u c t

105 105 105 104 106 105

0.1 105 104

1013 108 1010 1010 106 107

106 105 106

tan = 50

u c t

104 104 104 103 104 104

1 103 103

1011 106 109

108 104 105 104 103 104

Table 1. Hierarchies predicted for the B = 1 R-parity violating coupling, under the full MFV hypothesis [5, 6] and under its holomorphic restriction [9]. In this latter case, we adopt a slightly looser denition to account for possible RGE e ects and to stabilize the hierarchies under electroweak corrections (see the discussion in the main text; all these numbers are taken from ref. [5, 6]). Because IJK is antisymmetric under J K, its entries can be put in a 3 3 matrix form with I = u, c, t

and JK = ds, sb, db.

structures shown in eq. (1.2). In particular, the holomorphic restriction introduced in ref. [9] allows for the rst term only,1 and further forbids introducing avor-octet combinations like YuYu and YdYd. This last restriction is not RGE invariant though [13]. If the dynamics at the origin of the avor structures take place at some very high scale, we need to relax the holomorphic constraint. Further, from an e ective point of view, such YuYu and YdYd insertions occur at the low scale through electroweak corrections. So, in the following, we will denote by holomorphic the slightly loser hierarchy derived starting with LMNYILuYJMdYKNd, but allowing for additional non-holomorphic YuYu and YdYd spurion insertions (see table 1).

It is clear from table 1 that no matter the precise MFV implementation, the largest BNV couplings are always those involving the top (s)quark. Those with up or charm(s)quarks are extremely small, essentially because the epsilon tensor antisymmetry forces them to be proportional to light-quark mass factors (see eq. (1.2)). This permits to satisfy all the low energy constraints from proton decay, dinucleon decay or neutron oscillations, even for squark masses below the TeV scale [3, 5, 6, 9]. In this context, it is worth to stress that by construction, the MFV hierarchies are stable against electroweak corrections. So, the MFV implementation can be interpreted as a way to maximize the IJK coupling for each I, J, K. For example, if tds exceeds the value shown in table 1, it may induce a larger e ective uds coupling through SM or MSSM avor transitions, and thereby conict with experimental constraints.

1.2 Search strategy at colliders

The presence of the RPV couplings deeply alters the supersymmetric collider phenomenology, and none of the sparticle mass bounds set in the R-parity conserving case are expected to survive. So, it is our purpose here to analyze the signatures of the MSSM supplemented

1For recent discussions of possible dynamical origins for this holomorphic MFV prescription, see refs. [1012].

JHEP10(2013)068

with the UDD coupling of eq. (1.2), under the assumptions that follows the hierarchies shown in table 1. Before entering the core of the discussion, let us expose our strategy.

Since low energy constraints allow some of the BNV couplings to remain relatively large, no supersymmetric particle is expected to live for long. Except in a small corner of parameter space (to be detailed later), only SM particles are seen at colliders. The simplest amplitudes with intermediate (on-shell or o -shell) sparticles are thus quadratic in the BNV couplings, and correspond either to B = 0 or B = 2 transitions. Typically,

the former takes the form of enhancements in processes with SM-allowed nal states, like tt+ jets or multijet processes. Except if a resonance can be spotted, these are rather nonspecic signatures, and one must ght against large backgrounds. On the other hand, the B = 2 channels have much cleaner signatures which, to a large extent, transcend the

details of the MSSM mass spectrum. Indeed, regardless of the underlying dynamics, the MFV hierarchy strongly favors the presence of two same-sign top quarks in the nal state. A sizable same-sign lepton production is therefore predicted. At the same time, the initial state at the LHC has a B = +2 charge since it is made of two protons. As analyzed model-independently in ref. [14], this can induce a signicant negative lepton charge asymmetry, which is dened as

(pp ++ + X) (pp + X)

(pp ++ + X) + (pp + X)

JHEP10(2013)068

. (1.3)

Observing A < 0 would not only point clearly at new physics, but also strongly hint at baryon number violation. Indeed, the SM as well as most new physics scenarios generate positive asymmetries.

In the present paper, we will thus concentrate on this same-sign dilepton signal and its associated charge asymmetry. The other prominent RPV signatures, namely multijet resonances and R-hadron states, are described in the next section. To quantify the relative strengths of these signatures, it is necessary to analyze in some details the various mass hierarchies and decay chains. This is done in section 3, where the most relevant degrees of freedom are identied (the calculations of the squark, gluino, and neutralino decay rates in the presence of the couplings are briey reviewed in appendix A). We then show in section 4 how this information permits to set up a simplied framework. In section 5, we use this benchmark to translate the current experimental limits into constraints on sparticle masses, and to analyze the sensitivity of the future 14 TeV runs. Finally, our results are summarized in the conclusion.

2 Characteristic signatures of the R-parity violating MSSM

In the R-parity conserving case, the simplest production mechanisms for supersymmetric particles at the LHC are driven by the supersymmetrized QCD part of the MSSM. Further, processes like d d

~d ~d or g g have very large cross-section when the on-shell

~d or

production is kinematically accessible, hence the tight bounds already set on these particle masses. As stressed in the introduction, these bounds assume the presence of a signicant missing energy in the nal state and only hold if R parity is conserved.

When the largest RPV coupling is smaller or comparable to S, squarks and gluinos are still mostly produced in pair through QCD processes. The main non-QCD mechanism

g g

q~ q q~

g g

( )

a ( )

( )

g q~

( )

Figure 1. Some dominant leading-order strong (a d) and RPV (e) production mechanisms of

squarks and gluinos at the LHC. Processes with initial gluons or proton valence quarks, q = u, d, are favored by the parton distribution functions. We also show the next-to-leading order resonant squark production mechanism (f) because the dominant RPV couplings, shown as red dots, involve either the t, d, s avors in the full MFV case, or t, d, b; t, d, s; and t, s, b avors in the holomorphic MFV case, and thus the diagram (e) necessarily involves at least one sea quark.

yielding sparticles is the single squark resonant production, which requires less center-of-mass energy. At the LHC, the most abundantly produced sparticle states are thus (considering for now the full MFV hierarchy, see table 1):

u u L,RL,R , d d

~dL,R ~dL,R , u d L,R

JHEP10(2013)068

~dL,R ,

g g , g g ~qL,R ~qL,R , (2.1) s d ~tR ,and are shown in gure 1. The main di erence with the R-parity conserving case is that once the couplings are turned on, each of these sparticles initiates a decay chain ending with quark nal states, resulting in a signicant hadronic activity instead of missing energy. If we assume that the charginos and sleptons are heavier than squarks, gluinos, and the lightest neutralino (denoted simply as ~

0 ~

01 in the following), then we can identify three main characteristic signatures in this hadronic activity:

1. Top-quark production including same-sign top pairs. Because the dominant IJK couplings are those with I = 3, most processes lead to top quarks in the nal states (see gure 2). For example, we have ~d ts or, ~

0 t d s, t

ds. Even the stop can

decay into top-quark pairs if ~t t or ~t ~

0 t is kinematically open (see gure 2c).

For all these modes, a crucial observation is that the production of same-sign top pairs is always possible thanks to the Majorana nature of the gluino and neutralino. Despite its relatively small 5% probability, the same-sign dilepton signature is best suited for identifying such nal states. There are several reasons for this. First, charged leptons are clearly identied in detectors and avoid jet combinatorial background. Second, they allow to determine almost unambiguously the sign, and therefore the baryon number, of the top quarks they arose from. Finally, irreducible backgrounds are small as same-sign dilepton production is rare in the SM. So, this is the signature on which we will concentrate in the following (see also refs. [1517]).

Figure 2. (a d) Examples of mechanisms leading to same-sign top pair nal states, starting from

the dominant QCD processes of gure 1. (e g) Examples of production mechanisms leading to

light-quark jet nal states.

2. Di- or trijet resonances built over light quarks and maybe a few b quarks. A priori, dijets could originate from squark decays and trijets from gluino or neutralino decays. But with MFV, only up-type intermediate squarks can lead to light-quark jets, since the other sparticle decay products always include a top quark. The simplest process is thus the B = 0 resonant stop production with a dijet nal state (see gure 2f). But since the electric charge of a jet is not measurable, the B nature of the transition cannot be ascertained and QCD backgrounds appear overwhelming. Nevertheless, given the potentially large cross sections of the strong production processes depicted in gure 1, such an enhanced jet activity could be accessible experimentally [1821], and has already been searched for at colliders (see e.g. refs. [22, 23]).

3. Long-lived exotic states, the so-called R-hadrons built as hadronized squarks or gluinos ying away [24]. Such quasi-stable exotic states have already been searched for experimentally, excluding squark masses below about 600 GeV and gluino masses below about 1 TeV [25]. But, as will be detailed in the next section, R-hadron signatures are rather di cult to get once MFV is imposed. Indeed, some RPV couplings are large and all sparticles can nd a way to use them for decaying. For example, if tds 0.1, then, ~

0 t d s, t

ds proceeding via a virtual squark or

ds mediated by a virtual gaugino and a virtual squark (see gure 2d) are kinematically available and occur rather quickly for masses below 1 TeV (this is also true for a slepton LSP, see appendix A.3). Note, however, that very large gluino (or neutralino) lifetimes can always be obtained by increasing the squark masses well beyond the TeV scale, as for example in the split SUSY scenario [26, 27].

The relative and absolute strengths of these signals depend crucially on the MSSM mass spectrum. To proceed, we analyze in the next section the di erent spectra and corresponding decay chains in some details. This is a rather technical discussion, further complemented by the decay rate calculations in appendix A, whose main outcomes are

JHEP10(2013)068

~qL,R q t d s, q t

depicted in gures 3 and 4. The former shows that most sparticle decay chains end with top quarks, while the latter shows that the LSP lifetimes are nearly always short enough to avoid R-hadron constraints. Provided these two pieces of information are kept in mind, the reader less inclined to go through all the details may wish to directly jump to section 4, where our simplied setting is put in place.

3 Sparticle decay chains and lifetimes

The various possible cascades are depicted in gure 3. With charginos and sleptons decoupled, two alternative cases can be distinguished depending on whether the gluino or the squarks are the lighter.

3.1 Gluino lighter than squarks

Let us concentrate rst on the lower-left corner of this diagram. Still assuming that QCD processes dominate over RPV ones, the decay chains preferentially start by ~q q when

gluinos are lighter than squarks. These transitions are overwhelmingly avor conserving when MFV is enforced. If the gluino is the LSP, it then decays through the RPV coupling: t d s, t

ds (the full MFV hierarchy is assumed for now). If the lightest neutralino is the LSP, it is produced via q q ~

0, ~q q ~

0, as well as directly from electroweak

ds. Along these chains, the branching ratios are all close to 100%, except for the electroweak ~qR q ~

0 with which the fastest direct

Note that the partial widths of the gluino and neutralino are fairly large. Assuming the lightest neutralino is dominantly a bino, taking all squarks degenerate and neglecting mt/M~g,~0 as well as higher powers of M~g,~0 /M~q (see the discussion in appendix A.2), we get

t d s 3SM~g5122 | tds|2

M4~gM4~q, (3.1)

~0 t d s M~0 |N1B|21282 cos2 W | tds|2

M4~0M4~q. (3.2)

Numerically, for M~q1 TeV and M~g M~

0 300 GeV, these widths are ~g (104 GeV) | tds|2 and ~0 (105 GeV)| tds|2 (when the lightest neutralino is a pure bino, |N1B| =

1). We do not consider here the split-SUSY scenario [26, 27] where squarks are much heavier than the gluino or neutralino, so these numbers represent the minimum lifetimes for these particles. They are short enough to circumvent the already tight experimental bounds set on R-hadrons [25]. Actually, except at low tan and with the holomorphic MFV hierarchy (see gure 4), these sparticles even decay too quickly to leave noticeable displaced vertices.2

2If the gluino or neutralino are lighter than the top quark, then they decay into three light quarks thanks to subdominant RPV couplings. In the holomorphic case at low tan , the lifetimes could then be su ciently large to generate R-hadron signals for a gluino LSP, or monotop signals from ~t ! t ~

~0 for a

quasi stable neutralino LSP ying away. We will not consider these scenarios here [29].

JHEP10(2013)068

processes, and decays again as ~

0 t d s, t

RPV decays ~qR q q could compete.

~ c~0

l qq~

q ql

All squarks LSP

Some squarks LSP

q q

~ c~0

~ ~

q q qq q

q q W

l tt~

l qq

q qt

u ,c

L,R

d ,b

L,R

d ,s

L,R

Stop LSP

t~1

q ql

~ *

Gaugino LSP

~ c~0

l t,t+jj

t jj

q jj

q t+j

l t,t+jj

JHEP10(2013)068

t,t+jets

jets

t+jets

Figure 3. Decay chains of the squarks, gluino, and lightest neutralino down to quark-only nal states, depending on whether the gauginos, the stop, some of the squarks, or all the squarks are the lightest supersymmetric particles. The symbol () denotes a real (virtual) gluino or neutralino. For each squark, the relative strengths of the R-parity conserving (green and blue) and R-parity violating (red) transitions depend on the details of the mass spectrum as well as on the MFV hierarchy. In particular, whenever the gluino (and to some extent, neutralino) is too heavy to be produced on-shell (green), its virtual exchange opens some decay channels (blue) competing with the direct RPV decay processes (red). In the full MFV hierarchy, where tds is the largest RPV coupling, the jets arise mostly from s and d quarks. In the holomorphic case, some of them are built upon b quarks instead.

3.2 Squarks lighter than the gluino

As shown in gure 3, the situation is rather involved in this case. As a starting point, let us imagine that all the squarks are precisely degenerate in mass while both the gluino and neutralino are heavier. There are then neither mixings nor transitions among the squarks. Instead, the right-handed squarks decay directly to quarks thanks to the RPV couplings, while the left-handed squarks need to go through a virtual gluino or neutralino to do so (see gure 2d):

dJ dK

M~uIR

8 |

IJK|2 , (3.3)

IRIL

uI + uIt d s uIt

2SM~uIL,R

66003 |

tds|2

M2~q

M2~g

, (3.4)

and similarly for ~dIL,R, where again mt/M~q and higher powers of M~q/M~g are neglected. Remark that even though the Majorana gluino decays to t d s and t ds with equal probability, ~qIR decays mostly to top quark and ~qIL to anti-top quark because the ~qIR qIt

and ~qIL qIt d s rates scale like M4~q/M4~g instead of M2~q/M2~g (more details, as well as the

rates for the neutralino-induced processes can be found in appendix A.1 and A.3). Numerically, for M~g 1 TeV and M~q 300 GeV, the four-body decay width is larger than about

(108 GeV)|

tds|2, see gure 12 in the appendix. So, the squarks are not viable R-hadron

candidates when follows the full MFV hierarchy. Note however that the two-body decay

4000

400

3000

300

M[GeV]

2000

200

1000

100

0 0 1000 2000 3000 4000

100 200 300 400

M [GeV]

JHEP10(2013)068

Figure 4. Colored LSP partial widths in the holomorphic MFV case with tan = 5. Labels stand for log10( [GeV]). Specically, the largest RPV couplings

3IJ [lessorsimilar] 105 dominate everywhere

except in the low mass region where the top channels get kinematically suppressed and the impact of the subdominant RPV couplings 2IJ [lessorsimilar] 106 begins to be felt. Below the diagonal, the gluino is the LSP and decays via a virtual squark, while above the diagonal, the plots show the width of the most stable squarks, assuming it decays exclusively through a virtual gluino and a virtual squark. As explained in the text, this requires turning o the left-right squark mixing terms so as to close the decay channel of eq. (3.7). Phenomenologically, widths below 1016 GeV (10 ns) can lead to R-hadron signals [25], those below 1014 GeV (0.1 ns) could render the top identication di cult (because of the required b tagging [28]), while values up to a few 1012 GeV (0.001 ns) could lead to noticeable displaced vertices [9]. Note that max( 3IJ) and max( 2IJ) are the smallest in the holomorphic MFV case with tan = 5, but the plots for any other values can easily be inferred since all decay rates are quadratic in . For example, all the widths are 34 100 times larger if

tan = 15. In the full MFV case, but still at tan = 5, the widths above (below) the top-quark threshold are 108 (104) times larger, and even observing displaced vertices becomes impossible over most of the parameter space.

rates of the right-handed squarks span several orders of magnitude. In particular, for light avors, the four-body channels sometimes dominate when M~g is not too large. This is particularly true when the neutralino is lighter than squarks, in which case most of them decay rst to neutralinos, which then decay to t d s or t ds.

The introduction of realistic squark mass splittings complicates this picture. Under MFV, the squark soft-breaking terms are xed in terms of the Yukawa couplings as [7, 8]

m2Q = m20

h1 YdYd YuYu . . .i,

m2U = m20

1 Yu h1 YdYd YuYu . . .iYu ,

m2D = m20

1 Yd

h1 YdYd YuYu . . .i Yd

, (3.5)

Au = A0 Yu

h1 YdYd YuYu . . .i,

h1 YdYd YuYu . . .i.

As in eq. (1.2), indicates that arbitrary order one coe cients are understood for each

term. In this way, avor changing e ects are consistently tuned by the Cabibbo-Kobayashi-

Ad = A0 Yd

Full Holomorphic tan 5 50 5 50

(~q)4bodymin 1010 108 1018 1014 ( ~dR) 0.1 10 1011 107

( ~dL)dir 1010 106 1020 1014

( ~dL)mix 1015 1011 1017 1011 (R) 0.1 10 109 105

(L)dir 107 103 1015 109

(L)mix 1012 108 1014 108 (~bR) 107 105 1010 105

(~bL) 1010 106 1012 106

Table 2. Order of magnitude estimates of the squark decay widths (in GeV) when only the RPV modes are kinematically open, setting all squark masses at 300 GeV, and assuming the MFV hierarchies shown in table 1. The four-body decay widths quoted in the rst line, corresponding to eq. (3.4) with a gluino mass of 1 TeV, are universal and represent the upper limits for all the squark lifetimes. The superscripts dir refers to the direct ~qIL ~qIR qJ qK decay channel, eq. (3.6),

and mix to those allowed by the avor mixings in the squark soft-breaking terms once the MFV prescription is imposed, eq. (3.7). For ~tL and ~bL, these two mechanisms yield the same widths. Note that the tan scaling of the partial widths can be easily inferred from the values given for tan = 5 and 50.

Maskawa (CKM) matrix, and supersymmetric contributions to the avor-changing neutral currents end up su ciently suppressed to pass experimental bounds.

The mass spectra induced by the MFV prescription are similar to those obtained starting with universal GUT boundary conditions but for two crucial di erences [30]. First, because of the O(1) coe cients, the leading avor-blind terms of m2Q, m2U, and m2D need not

be identical at any scale. Second, the third generation squark masses can be signicantly split from the rst two, especially when tan is large. This originates from the hierarchy of YuYu and YdYd: both have as largest entry their 33 component. A typical MFV spectrum at moderate tan is thus made of the quasi degenerate sets {L,L,

~dL,L,~bL},

{R,R}, {

~dR,R,~bR}, together with the stop eigenstates ~t1,2 which are split from their

avor partners by the large A33u. When tan is large, the sbottom mass eigenstates ~b1,2 are also split from their avor partners. Note that such a large stop mixing may actually be required to push the lightest Higgs boson mass up to about 125 GeV [31].

The MFV prescription for the squark mass terms impacts the decay chains in three ways. First, ~t

~bW or ~b ~tW may possibly open. Weak decays are irrelevant for the

other squark avors becauseL,L, ~dL, andL are essentially degenerate, and their LR mixings are small. Note that when MFV is active, avor-changing weak decays of the ~t and ~b are suppressed by the small CKM angles, and can be safely neglected. Second, squarks can cascade decay among themselves through the three-body ~q q q~q processes

Full Holomorphic tan 5 50 5 50

(~q)4bodymin 1010 108 1018 1014 (R) 109 107 1015 1011

(L)dir 1019 1017 1025 1021

(L)mix 1010 104 1018 1010 (R) 107 105 1011 107

(L)dir 1012 1010 1016 1012

(L)mix 108 102 1016 108 (~tR) 0.1 10 109 105

(~tL) 0.1 10 109 105

JHEP10(2013)068

mediated by a virtual3 gluino or neutralino. This is relevant only for those squarks having suppressed RPV decays like for exampleL,R u

d ~dR if4 (m2D)11 < (m2Q,U)11. Third, the RPV two-body decay modes open up for the left-handed squarks thanks to the non zero (Au,d)II, and to the avor mixings present in m2Q and Au,d. Taking the up-type squarks for deniteness and assuming tds dominates, their partial decay widths are

IL IR dJ dK

dir

M~uIL 8

muI

IJK

2 , (3.6)

IL ~tR ds

mix

IL ~tL ~tR ds

mix

M~uIL 8

mt vu

m2b v2d

VIbV tb tds

, (3.7)

where we set m0 A0. In the I = 1 case, the direct channel is extremely suppressed by the

tiny left-right mixing A11u mu/vu and RPV couplings

uJK. By contrast, the indirect channel tuned by tds becomes available at the relatively modest cost of |VubV tb| 103

thanks to the avor mixings in m2Q and Au (specically, to the YdYd terms in eq. (3.5)). Note that YdYd is proportional to m2b/v2d, so (L)mix has a very strong tan6 dependence once accounting for the tan scaling of (this further increases to a tan8 dependence in the holomorphic case). It actually ends up larger than (R) when tan [greaterorsimilar] 10 (see table 2). Indeed, a similar decay mechanism forR is never competitive once MFV is imposed because YdYd occurs in m2U only sandwiched between Yu and Yu. So, (m2U)13 is proportional to the tiny up-quark mass andR ~tR

ds is very suppressed.

As said above, MFV is compatible with a stop LSP, since it naturally allows for a large splitting of the third generation squarks. In that case, most decay chains still end with a top quark, see gure 3. Indeed, though the RPV decay ~t jj is top-less and very fast,

the stops arise mostly from the avor-conserving decays of heavier sparticles, and are thus produced together with top quarks. For example, the gaugino decays exclusively to t, t+jj independently of whether it is a true LSP or a yet lighter stop is present.

3.3 Combining sparticle production mechanisms with decay chains

With the full MFV hierarchy, most decay chains end up with a top quark (see gure 3). Further, without large mass splittings, the sparticle decay widths are large enough to avoid R-hadron constraints. Actually, most decays are even way too fast to leave displaced vertices (see gure 4).5 So, given the production mechanisms of eq. (2.1), the supersymmetric processes can be organized into two broad classes. If the rst-generation squarks are heavier than the gluino, then there are no nal states made entirely of light-quark jets:

M~g < m2Q,U,D : g g (t t, tt) + 4j/6j/8j , (3.8)

3This remains true when the gluino or neutralino is real with a mass lying somewhere in-between the squark states.

4Here and in the following, we denote a specic squark mass hierarchy in terms of the corresponding soft mass term hierarchy, even though it is understood that squark masses do not depend only on these parameters.

5Note, though, that a colored LSP would live long enough to hadronize.

JHEP10(2013)068

with the number of jets increasing when gluinos rst cascade decay to neutralinos. Note that we already discarded the t t + jets nal state, since it would correspond to a B = 0 process.

Conversely, if the squarks are lighter than the gluinos, then most but not all decay chains terminate with a top quark. So, most of the processes initiated by the proton u and/or d quarks lead to same-sign top-quark pairs:

m2D < m2Q,U, M~g : d d

~dR ~dR tt+ 2j , m2Q < m2D,U, M~g : d d

~dL ~dL tt+ 2j/4j/6j , u d L

~dL tt+ 4j/6j ; t + 3j , (3.9) u u LL tt+ 6j ; 4j ,m2U < m2Q,D, M~g : u u RR t t + 6j ; 4j ,

where we neglected the suppressed decayLL t t + 6j andRR tt + 6j (see

the discussion in appendix A.3). Again, the number of jets increases when at least one neutralino is lighter than the squarks. In these equations, the comparisons between m2Q, m2U, and m2D are understood to apply to their 11 and 22 entries which give, to an excellent approximation, the rst two generation squark masses (see eq. (3.5)).

Whatever sparticle production mechanism dominates, the precise production rate of same-sign top-quark pairs depends on whether the squarks, when they are not the lightest, prefer to undergo their RPV decay or, instead, to cascade decay down to other squarks, which in turn may or may not produce same-sign top pairs. For example, when m2D < m2Q,U, it is quite possible thatL,R, and ~dL all decay into ~dR, which then decays to t+j.

Conversely, when m2U < m2Q,D and M~g,~0 is large, we may be in a situation where all of them but ~dR cascade down toR, which then produces two jets. In this case, only ~dR ~dR produces top pairs. So, depending on the MSSM mass spectrum, the amount of same-sign top pairs can span more than an order of magnitude.

With the holomorphic MFV hierarchy, the above picture remains valid, at least qualitatively. The decay chains still mostly end up with top quarks and the amount of same-sign top pairs emerging from the production mechanisms of eq. (2.1) is not much a ected. There are four di erences worth noting though. First, some light-quark jets are replaced by b jets in all nal states. Second, the branching ratios for the three left-squark decay modes, eq. (3.4), (3.6), and (3.7), are a ected, hence the decay chains do not necessarily follow the same paths as with the full MFV hierarchy. Third, all couplings are now much smaller than , so the direct RPV decays are systematically subdominant whenever ~q q ~

01 or

01 are kinematically open (assuming ~

01 is essentially a bino). Same-sign top-quark pairs still arise, but are in general accompanied by many more jets. Finally, a light LSP, whether it is a gluino, neutralino, or a squark, can have a large lifetime when tan is small, even for moderate mass hierarchies (see gure 4). This is the only corner of parameter space in which R-hadron constraints could play a role.

Specically, looking at table 2, the lifetimes are always below about 1 s. This is rather short, so we should use the bounds the Atlas collaboration sets using the inner detector only [25], which requires the total width of the sparticle to be below about 1016 GeV

q q ~

JHEP10(2013)068

(see gure 4). Such a lifetime for the squarks is a priori possible only for theL and ~dL. It further requires tan [lessorsimilar] 10 and A0 [lessorsimilar] m0, otherwise the two-body decay rates eq. (3.7) are above 1016 GeV even for M~uL, ~dL as low as 300 GeV. Both these conditions appear contradictory to the requirements of a rather large Higgs boson mass [31], which asks for a not too small tan and relatively large trilinear terms. So, even with the holomorphic MFV hierarchy, squarks do not appear viable as R-hadron candidates. Turning to the gluino, although its lifetime can always be made long enough by increasing the squark masses, this nevertheless requires pushing them to very large values. For tan = 5 and M~g = (250, 500, 1000) GeV, the gluino width is below 1016 GeV for M~q [greaterorsimilar] (1, 5, 13) TeV.

This is the range excluded by the Atlas bound. Note that the squark and gluino lifetimes increase if their mass is below mt, since this shuts down the dominant RPV decay mode.

But the Atlas bounds on the squark and gluino masses are already well above mt, so this

region is excluded. We thus conclude that the R-hadron constraints play no role over the mass range over which the dilepton signal will be probed in the following, which goes from M~g, M~q 200 to about 1100 GeV.

4 Simplied mass spectrum and analysis strategy

In view of the complexity of the decay chains discussed in the previous section, it is very desirable to design a simplied analysis strategy. For instance, the exact squark decay chains depend on the many MSSM parameters tuning the squark masses and the three decay modes of eq. (3.4), (3.6), and (3.7), so one should in principle perform a full scan over these parameters.

The situation is, however, more simple than it seems. Indeed, given that there are only two broad classes of decay chains, it is possible to simulate them generically by introducing only two mass scales, M~g and M~q, with M~q denoting the rst generation squark mass scale.

Though not immediately apparent, this is su cient to encompass in a very realistic fashion the dominant decay chains for most mass spectra. Indeed:

M~g < M~q . This sector describes generically the situation where squarks are heavier than the gluino, and is dominated by the g g production mechanism. Assuming

neutralinos are heavier, each gluino then decays exclusively to (t, t) + 2j. There are as many t t as tt pairs so the lepton charge asymmetry vanishes,

(p p tt+ 4j) : (p p t t + 4j) 1 : 1 . (4.1) Note that (g g ) = 2(g g (t t, tt)+4j), expected from the Majorana

nature of the gluinos, is not always strictly true, especially when the gluino width is large [32]. The reason is to be found in the chirality of the RPV and gluino couplings, which selects either the /

p or the M~g terms of the gluino propagators (see the discussion in appendix A.3). The signal is similar if the neutralino replaces the gluino as LSP, with the same-sign top quarks produced through g g

0 ~

~ 0 + 4j (t t, tt) + 8j. The top-quark energy spectra would then be slightly

softer because of the longer decay chains. Our bounds on the gluino mass are, in

JHEP10(2013)068

this case, only approximate. On the other hand, the precise squark mass spectrum is almost completely irrelevant since it a ects only the gluino (or neutralino) lifetime, not its decay modes. This remains true even if the stop is the LSP. When the other squarks are heavier than the gauginos, for instance, the gluinos almost exclusively decay through t

t, t~t (t, t) + 2j.

M~g > M~q . This sector describes generically the situation where rst-generation squarks are lighter than gauginos. Looking at all the processes in eq. (3.9), the crucial observation is that d d

~dR ~dR tt+ 2j is always active, while the other squark intermediate

states may or may not lead to same-sign top pairs, depending on the MSSM parameters. So, to account for a large range of possibilities, we span from the pessimistic situation where p p

~dR ~dR tt+ 2j is the only top-pair producing channel, to the

optimistic situation where d d

~dL ~dL tt+ 2j and d d

~dR ~dL tt+ 2j are also active, with ~dR,L both of mass M~q and with unit branching fraction to t+ j. The much longer ~dL lifetime is not directly relevant, at least as long as it decays within the detector.6 Note that the p p

~dR ~dL channel would be the only one to survive if gluinos were Dirac particles [33]. In any case, since the d proton PDF is signicantly smaller than that of the d, the lepton charge asymmetry is close to maximally negative:

p p ~dR,L ~dR,L tt+ 2j : p p ~dR,L ~dR,L t t + 2j 1 : 0 . (4.2)

In principle, the number of top pairs could further be increased by nearly an order of magnitude if up quarks come into play. For simplicity and since these modes give rise to softer nal states of higher jet multiplicity, we prefer to disregard them. In addition, realistic situations probably lie somewhere between our pessimistic and optimistic settings, with some top pairs coming from both ~dL andL,R but with

B( ~dL t+ j) and B(L,R t+ 3j) < 1. Note also that, if the contribution of

u u t t + 6j is signicant (for intermediateL, this requires a rather light

gaugino), or if all the four-body nal states are strongly favored by a light neutralino, the lepton charge asymmetry could be somewhat diluted.

M~g M~q . In this region, in addition to g g and d d

~dR tt+ 3j is competitive. In the optimistic case, an equal amount of

top-quark pairs is produced through the g d

~dL tt+ 3j process. As for the

d d

~d ~dprocesses, the proton PDF strongly favors negative lepton pair productions:

p p ~dR,L tt+ 3j :

1 : 0 . (4.3)

Compared to the other cases, it should be stressed that the decay chains in the M~g M~q region can be rather complicated. Indeed, squarks are not precisely degenerate

6With the holomorphic hierarchy, when tan [lessorsimilar] 15 (or a bit lower if A0 > m0 at the TeV scale), the ~dL lifetime could be above about 0.1 ns (see gure 4). At that point, the identication of top-quark pairs through same-sign leptons plus b-jets starts loosing e ciency because the b tagging requires a secondary vertex no farther than a few centimeters away from the primary one [28].

JHEP10(2013)068

~dR ~dR, the mixed production

g d

p p ~dR,L t t + 3j

in mass, so this region includes compressed spectra with the gluino (or neutralino) mass lying in-between squark masses. Overall, the amount of top pairs should not be very signicantly reduced, but their production may proceed through rather indirect routes. For instance, one of the worst case scenario occurs when m2U [lessorsimilar] M~g [lessorsimilar] m2D,Q.

The ~dR,L d decay competes with

~dR,L t+ j and u, c competes with t ~t, thereby strongly depleting the amount of directly produced top pairs. At

the same time, u u RR more than replenishes the stock of top pairs since the

four-body decay modes entirely dominate when M~g M~q (and there are more u

quarks than d quarks in the protons). This example shows that xing the ne details of the mass spectrum is in principle compulsory to deal with compressed spectra, but also that our pessimistic estimates based only on the g g tt + 4j,

g d

~dR tt+ 3j, and d d

~dR ~dR tt+ 2j production mechanisms should

conservatively illustrate the experimental reach.

Thanks to the above simplications, we only need to simulate the processes of eqs. (4.1), (4.2), and (4.3). In practice, we use the FeynRulesMadGraph5 software chain [34, 35] to produce leading order and parton level samples for the 8 and 14 TeV LHC. The squark and gluino masses M~q and M~g are then varied in the 2001100 GeV range while the neutralino, charginos, and sleptons are decoupled. In our analysis, we are not including the single-stop production mechanism (see gure 1). The reason is that it leads to same-sign top pairs only for a lighter gluino, in which case it is subleading compared to g g .

We also neglect the subleading q q production mechanisms. If only the neutralino

is lighter than the stop, there could be some same-sign top events only when ~t jj is

suppressed, like in the holomorphic case. We do not study that alternative here. We are also disregarding electroweak neutralino pair productions, or neutralino-induced squark production mechanisms, e.g., d d

~d ~d via a neutralino (see gure 1). Both can generate same-sign top pairs, but are entirely negligible compared to the strong processes given the gluino mass range we consider here. So, neither the stop nor the neutralino are a ecting the production mechanisms. In addition, we explained before that they do not a ect the decay chains su ciently to alter the same-sign top-quark pair production rate. So, for the time being, our signal is totally insensitive to both the stop and neutralino masses.

Throughout the numerical study, the RPV couplings are kept xed to either tds = 0.1 for the full MFV case, or tbs = 103 and tds,tdb = 104 for the holomorphic case, with all the smaller couplings set to zero. It should be clear though that the overall magnitude of these couplings does not play an important role. It a ects the light sparticle lifetimes but not directly their branching ratios or their production rates. This is conrmed by the similarity of the results obtained in the next section with either the full or holomorphic hierarchy. Besides, since the sparticle widths play only a subleading role, we compute them taking all the squarks degenerate in mass.

This benchmark strategy is naturally suited to a two-dimensional representation in the M~q M~g plane (see gure 5). But, it must be stressed that even if this representation

is seemingly similar to that often used for the search of the R-parity conserving MSSM, the underlying assumptions are intrinsically di erent and far less demanding in our case.

JHEP10(2013)068

s [c37] [c37] [c37]

[c37] [c37] [c37] L

i R

i i

pp gg,gd ,d d

( ) +

( , ) +

pp gg,gd ,d d tt tt

[c37] [c37] [c37]

[c37] [c37] [c37] i i i L

i R R

1000

200 200 300 400 500 600 700 800 900 1000

R+L

360

160

9.6

4.1

450

190

7.7

77 100

1000

10000

92 R+L

590

260

130

380

170

R+L

850 R+L

1300

550

260

330

290

2200

950

1300

1200

1300

4600

7000

6900

6800

55000

54000

55000

54000

55000

54000

460 R R

R+L

220

640

320

180

110

980

520

310

200

140

110

1700

970

620

440

330

270

210

R R+L

120 R+L

230 200

3500

2100

1500

1100

940

830

770

730

R+L

8400

5900

4500

3800

3400

3200

3100

29000

23000

19000

18000

17000

2000

20000

16000

160000

150000

140000

130000

900

800

700

M g ~

600

500

400

300

200

200 300 400 500 600 700 800 900 1000

Mq~

JHEP10(2013)068

Figure 5. Sdown plus gluino production rate [fb] at the 8 TeV LHC computed at leading order with MadGraph5, and the corresponding rate for the same-sign top-quark pair production, with or without active ~dL (the grid of numbers corresponds to the former case). When the top-quark pair arises from down-type squarks, the rate is not reduced since B(

~dR,L ts) = 1. When it arises from g g , the reduction is close to two since B( t d s) = B( t

ds) = 1/2.

Indeed, by using these two mass parameters and only a limited number of super-QCD production processes, our purpose is to estimate realistically the amount of same-sign top-quark pairs which can be produced. Crucially, no scenario with relatively light squarks and/or gluino could entirely evade producing such nal states, and the experimental signals discussed in the next section are largely insensitive on how the top quarks are produced.

Finally, it should be mentioned that colored sparticle pair production is signicantly underestimated when computed at leading order accuracy (compare gure 5 with e.g. refs. [36, 37]), so the strength of our signal is certainly conservatively estimated. Our choice of working at leading order is essentially a matter of simplicity. Indeed, the whole processes are easily integrated within MadGraph5, including nite-width e ects. In addition, our main goal here is to test the viability of our simplied theoretical framework and its observability at the LHC, so what really matters is the reduction in rate starting from gure 5 and going through the experimental selection criteria. Of course, in the future, NLO e ects should be included to derive sparticle mass bounds. But, given the pace at which experimental results in the dilepton channels are coming in, we refrain from doing this at this stage.

5 Same-sign dileptons at the LHC

Both CMS [3842] and ATLAS [4347] have studied the same-sign dilepton signature at 7 and 8 TeV, and used it to set generic constraints on new physics contributions. Signal regions characterized by moderate missing energy, relatively high hadronic activity or jet multiplicity and one or two b tags are expected to be the most sensitive to same-sign tops plus jets.

5.1 Experimental backgrounds

In these searches, irreducible and instrumental backgrounds have comparable magnitudes. Irreducible backgrounds with isolated same-sign leptons and b jets arise from ttZ and ttW production processes. Their NLO cross sections [4850] amount respectively to 208 and 232 fb at the 8 TeV LHC. The di- and tribosons (W W , W Z, ZZ; W W W , W W Z, ZZZ)

plus jets productions also contribute, generally without hard b jet and sometimes with a third opposite-sign lepton coming from a Z boson. Positively charged dileptons dominate over negatively charged ones at the LHC when the net number of W bosons (the number of W + minus the number of W ) is non-vanishing. This feature is generic in the SM which communicates the proton-proton initial-state charge asymmetry to the nal state.

Instrumental backgrounds arise from the misreconstruction (mainly in tt events) of

(heavy) mesons decaying leptonically within jets,

hadrons as leptons,

asymmetric conversions of photons,

electron charges (if a hard bremsstrahlung radiation converts to a e+e pair in which

the electron with a charge opposite to the initial one dominates).

The rst three sources are often collectively referred to as fake leptons. The important contribution of b quark semi-leptonic decays in tt events with one top decaying semi-leptonically and the other hadronically is signicantly reduced when (one or) several b tags are required [38].

5.2 Selection criteria

We place ourselves in experimental conditions close to those of CMS, whose collaboration provides information (including e ciencies) and guidelines for constraining any model in an approximate way [3842]. We ask for semi-leptonic decays of the top quarks to electrons or muons, and further require:

two same-sign leptons with pT > 20 GeV and || < 2.4,

at least two or four jets (depending on the signal region) with pT > 40 GeV and || < 2.4,

at least two of these jets (three in one of the signal regions) to be b-tagged.

Still following CMS analyses, we dene in table 3 several signal regions (SR) with di erent cuts on the missing transverse energy /

ET and the transverse hadronic activity HT . The selection of an isolated lepton is taken to have an e ciency of 60% and the tagging of a parton level b quark as a b jet is xed to be 60% e cient too. These values have been chosen in view of the e ciencies obtained (see gure 6) using the pT -dependent parametrization provided by CMS. Note that, for b tagging, the value chosen is a few percent lower than those estimated in this way. With backgrounds under control, a higher number of isolated leptons from signal events could be selected by lowering the cut on their pT or by modifying the isolation requirement [15]. On the other hand, the pT -dependent parametrization of

JHEP10(2013)068

Lepton efficiency in SR0 Lepton efficiency in SR8

b-tagging efficiency in SR0 b-tagging efficiency in SR8

1000

200 200 300 400 500 600 700 800 900 1000

1000

200 200 300 400 500 600 700 800 900 1000

0.61

0.62

0.63

0.64

0.65

0.64

0.61

0.62

0.63

0.64

0.65

0.63

0.6

0.61

0.62

0.63

0.64

0.63

0.62

0.6

0.61

0.62

0.63

0.62

0.6

0.61

0.62

0.61

0.6

0.61

0.6

0.60

0.59

0.58

0.61

0.62

0.63

0.64

0.65

0.64

0.61

0.62

0.63

0.64

0.65

0.63

0.6

0.61

0.62

0.63

0.64

0.63

0.62

0.6

0.61

0.62

0.63

0.62

0.6

0.61

0.62

0.61

0.59

0.61

0.6

0.60

0.6

0.59

0.58

900

800

700

M g ~

600

500

400

300

JHEP10(2013)068

Mq~

1000

0.64

0.65

0.66

0.65

0.64

0.65

0.66

0.65

0.64

0.65

0.66

0.65

0.64

0.65

0.64

0.65

0.64

0.63

0.64

0.63

0.62

0.65

0.66

0.65

0.64

0.65

0.66

0.65

0.64

0.65

0.66

0.65

0.64

0.65

0.64

0.65

0.64

0.63

0.66

900

800

700

M g ~

600

500

400

300

200

200 300 400 500 600 700 800 900 1000

200

200 300 400 500 600 700 800 900 1000

Mq~

Figure 6. E ciencies for isolated lepton identication (top) and b tagging (bottom) in signal region SR8 (left) and SR0 (right), using the pT -dependent parametrization provided by CMS [3842]. Since the RPV signal circumvents the signicant drop in e ciencies for low pT , these can be taken as constants in a good approximation. In our simulation, both of them are frozen at 60%.

the isolated lepton selection e ciency might not be reliable in regions where the tops can be boosted or when the hadronic activity of a typical event is important [17]. For our preliminary limit setting we will however keep constant e ciencies.

To assess the goodness of our parton level approximate selection, we compared it (relaxing the same-sign condition for leptons) to the total acceptance in SR1 quoted by CMS for SM tt events with semi-leptonic top decays. Our total acceptance of 0.20% (including top branching fractions) is compatible but lower than the (0.290.04)% quoted by CMS [3942].

So, at this step, the strength of our signal is probably conservatively estimated.

5.3 Current constraints and prospects

For several choices of squark and gluino masses, we count the number of events in each signal region and compare it with the 95% CL limits set by CMS assuming a conservative 30% uncertainty on the signal selection e ciency and using 10.5 fb1 of 8 TeV data [3942]. The corresponding exclusion contours in the M~q M~g plane are displayed in gure 7.

In the full MFV hierarchy case, we note that signal regions with low HT cuts perform well in the low mass range, where jets are softer. Everywhere else, SR8 characterized by no /

ET cut and a relatively high HT > 320 GeV requirement provides the best sensitivity. As

SR0 SR1 SR4 SR3 SR8 SR5 SR6 SR7 Min. number of b tags 2 2 2 2 2 2 2 3 Min. number of extra jets 0 0 2 2 2 2 2 0

Cut on HT [GeV] 80 80 200 200 320 320 320 200 Cut on /

ET [GeV] 0 30 50 120 0 50 120 50 Limit on BSM events 30.4 29.6 12.0 3.8 10.5 9.6 3.9 4.0

Table 3. Denitions of the signal regions used by CMS [3942] for same-sign dilepton searches. For each of them, the 95% CL upper limit on beyond the SM (BSM) events is derived from 10.5 fb1

of 8 TeV data, assuming a 30% uncertainty on signal e ciency and using the CLs method.

JHEP10(2013)068

Full MFV Holomorphic MFV

1000

400 200 300 400 500 600 700

900

800

M g ~

700

600

500

400 200 300 400 500 600 700

M g ~

Mq~

Figure 7. 95% CL exclusion contours in the M~q M~g plane derived from the CMS same-sign

dilepton search [3942]. The lower red contours are obtained with the contribution of the ~dR only while the upper blue contours assume an equal contribution of ~dR and ~dL (i.e., with identical branching ratios to ts). Importantly, M~q denotes the mass scale of the rst generation squarks, R,L and ~dR,L. The presence of a light stop or a light neutralino does not signicantly impact these exclusion regions. Finally, note that the R-hadron constraints in the holomorphic case are completely o the scale, requiring M~q greater than at least a few TeV.

expected, in the presence of R-parity violation, the SUSY searches requiring a large amount of missing energy are not the best suited. This can be understood from the shapes of the RPV signal and ttW + ttZ background in the HT /

ET plane (see gure 8). For squark and gluino masses close to the exclusion contour of SR8 (without ~dL contributions), the two missing energy distributions are very similar. For higher sparticle masses, the average /

ET is only slightly more important in signal events. On the other hand, a relatively good discrimination between signal and background is provided by the transverse hadronic activity HT . The jet multiplicity or highest jet pT may also provide powerful handles [15].

In the whole squark mass range, the SR8 limit excludes gluino masses below roughly 550 GeV. In the low- and mid-range squark mass region however, the bound varies signicantly depending on the contributions of ~dL to the same-sign tops signal. In the most unfavorable situation where ~dL contributions are vanishing, the gluino mass limit saturates around 800 GeV while it rises well above the TeV in the most favorable case where ~dL contributes as much as ~dR. Note that the same-sign squarks production cross section decreases with increasing gluino masses, so the bound will nonetheless reach a maximum there.

M M

= 400, = 750 GeV

M M

= 600, = 950 GeV

600

RPV

500

400

E T

300

E T

300

200

100

0 200 400 600 800 1000 1200

0 0 200 400 600 800 1000 1200

JHEP10(2013)068

M M

= 700, = 550 GeV

M M

= 900, = 750 GeV

600

SM RPV

600

SM RPV

500

400

E T

300

E T

300

200

100

0 0 200 400 600 800 1000 1200

Figure 8. Shape 1/ d2/dHT d /

ET [100 GeV ]2 of the RPV signal in SR0 and in the full MFV hierarchy case. The ~dL contributions to the top pair production are not included here. For comparison, the shape of the SM ttW + ttZ background is also shown. Those events are generated at leading order and parton level using MadGraph5 [35].

In the holomorphic MFV hierarchy case, the nal state b multiplicity is on average higher than with the full MFV hierarchy. Tagging at least two b jets is therefore much more likely and the limits slightly improve. SR7 where three b tags are required is then also populated by a signicant number of signal events and provides competitive bounds. Overall, this pushes the limit on sparticle masses higher, towards regions where the average /

ET of signal events slightly increases. There, SR3 and SR6 characterized by a higher /

ET > 120 GeV cut and very small backgrounds perform more and more e ciently. This is especially visible when the contributions of ~dL are signicant and further enhance the signal rate. For moderate sparticle masses though, SR8 still leads to the best limit.

We note that our exclusion regions in the holomorphic MFV case are somewhat more conservative than the M~g [greaterorsimilar] 800 GeV limit obtained in ref. [17]. To see this, rst note that the scenario analyzed there decouples all sparticles except the gluino and a top squark, the latter being the LSP. Same-sign top pairs are produced though p p with the

gluino decaying as t b s, t

b s via on-shell ~t squarks. As explained in section 4, such a scenario is covered by our simplied theoretical setting: it corresponds to the M~q

region of our plots. So, looking at gure 7, we get the lower M~g [greaterorsimilar] 630 GeV limit. We checked explicitly that it does not depend signicantly on whether the stop can be on-shell

or not. Even though the kinematics is di erent, the selection criteria are broad enough to prevent a signicant loss of sensitivity. Now, as can be seen in gure 5, our LO rate at M~g 800 GeV is about ve times smaller than that at 630 GeV, where our limit rests.

But, as said before, we do not include the NLO corrections. Comparing our gure 5 with ref. [36, 37], the rate at 800 GeV is strongly enhanced and nears that computed at LO for 630 GeV. In addition, there are other subleading but not necessarily negligible di erences in the two treatments, for instance: only the g g contribution to the gluino pair production has been considered here, the sensitivity is slightly di erent when stops are on or o their mass-shell, nite-width e ects are not included in ref. [17], and our simulation procedure is simpler, with for instance the isolated lepton identication and b tag e ciencies kept frozen at 60%.

To illustrate the perspectives of improvement on the mass bounds, the ducial 8 TeV cross sections for SR8 (currently providing the best sensitivity in most cases) and SR0 (the baseline selection) are displayed in gure 9. Improving the limits by a factor of ten could lead to an increase of the absolute bound on the gluino mass of the order of a couple of hundred GeV. The improvement would be the more signicant in the lowest allowed squark mass region where the limit on the gluino mass could increase by more than a factor of two. A similar gain would be obtained at the 14 TeV LHC if a bound on the BSM same-sign dilepton ducial rate comparable to the one obtained so far at 8 TeV is achieved. In this respect, it is worth to stress that the characteristics of the signal change as the sparticles get heavier. With increasing bounds on their masses, the signal regions with signicant missing energy should become competitive once adequate techniques are put in place to identify the boosted top quarks (see for instance refs. [5153]). Though a large fraction of the RPV signal is cut away from these regions, very tight limits can be set there since they are mostly free of backgrounds.

5.4 Charge asymmetries

As already mentioned, the irreducible ttW background features a predominance of positively charged dileptons over negative ones. More quantitatively, MadGraph5 [35] leading order SM estimates for the lepton charge asymmetry dened in eq. (1.3) are:

SR0 SR1 SR4 SR3 SR8 SR5 SR6

AttW+ttZ 0.26 0.28 0.29 0.36 0.26 0.28 0.35

JHEP10(2013)068

. (5.1)

The value in SR1 agrees well with the central CMS estimate of refs. [3942]. On the other hand, the RPV processes initiated by down valence quarks (that dominate the same-sign dilepton production when squarks are lighter than gluinos) are signicantly more probable than their conjugates, initiated by anti-down quarks. In the upper-left part of the M~qM~g plane, much more anti-top than top-quark pairs are therefore expected. This leads to a predominance of negatively charged dileptons and A approaches 1 for all , = e, ,

(see gure 10, where only electrons and muons are considered).

This observation has two important consequences. On the theoretical side, as already emphasized in ref. [14], such a negative asymmetry is a smoking gun for new physics and an

SR0, 8 TeV, full MFV

SR8, 8 TeV, full MFV

1000

200 300 400 500 600 700 800 900 1000

0.45

0.22

0.12

0.064

0.034

0.018

0.014

1.2

0.55

0.28

0.15

0.08

0.043

0.036

0.025

1.6

0.73

0.38

0.19

0.1

0.096

0.073

0.07

0.1

2.2

1.1

0.51

0.27

0.28

0.24

0.23

0.22

3.4

1.5

0.76

0.93

0.83

0.81

0.82

2.9

5.7

2.6

3.6

3.4

3.3

3.4

130

0.71

0.4

0.2

0.11

0.062

0.033

0.018

0.014

0.91

0.51

0.27

0.15

0.077

0.041

0.036

0.025

1.2

0.68

0.37

0.18

0.1

0.096

0.073

0.07

0.1

1.7

0.99

0.49

0.26

0.28

0.24

0.23

0.22

2.8

1.4

0.72

0.92

0.83

0.81

0.82

2.4

3.6

3.3

3.4

3.3

3.4

8.8

900

800

700

M g ~

600

500

400

300

200

200 300 400 500 600 700 800 900 1000 200

Mq~

JHEP10(2013)068

SR0, 8 TeV, holomorphic MFV SR8, 8 TeV, MFV

holomorphic

SR0, 14 TeV, full MFV SR8, 14 TeV, full MFV

1000

200 300 400 500 600 700 800 900 1000

2.1

0.51

0.27

0.15

0.078

0.04

0.024

2.7

1.3

0.66

0.36

0.19

0.095

0.071

0.1

2.9

3.4

1.7

0.92

0.46

0.23

0.21

0.22

2.6

1.3

0.62

0.71

7.9

3.8

1.8

2.6

2.5

2.6

2.5

6.1

240

1.3

0.75

0.4

0.22

0.13

0.068

0.034

0.024

1.7

0.98

0.53

0.31

0.16

0.081

0.07

0.071

0.1

2.3

1.4

0.78

0.4

0.19

0.21

0.22

3.5

2.1

1.1

0.52

0.71

0.7

0.71

3.3

1.5

2.5

900

800

700

M g ~

600

500

400

300

200

200 300 400 500 600 700 800 900 1000 200

Mq~

1000

200 300 400 500 600 700 800 900 1000

3.5

1.9

1.2

0.81

0.55

0.34

0.22

0.37

4.6

2.6

1.6

1.1

0.67

0.43

0.77

0.6

31 100

6.4

3.7

2.4

1.4

0.85

1.7

1.4

9.5

5.6

3.1

1.9

3.5

3.4

4.6

9.7

9.6

9.5

130

120

700

690

700

2.8

1.8

1.2

0.78

0.53

0.33

0.21

0.37

3.8

2.4

1.6

1.1

0.65

0.41

0.76

0.6

30 100

5.4

3.5

2.3

1.3

0.81

1.7

1.4

8.5

5.3

1.8

3.5

3.4

7.7

4.3

9.6

9.4

120

110

120

110

120

190

200

190

200

190

900

800

700

M g ~

600

500

400

300

200

200 300 400 500 600 700 800 900 1000 200

Mq~

Figure 9. Fiducial cross sections [fb] in the SR0 and SR8 signal regions for the same-sign dilepton RPV signal at the LHC. At 8 TeV, in SR8 (SR0), the 1 fb (2.9 fb) contour line correspond to the 95% CL set by CMS in [3942]. The red (plain) contours are obtained with the contribution of the ~dR only while those in blue (dashed) assume an equal contribution of ~dR and ~dL. Comparing with gure 5, the overall acceptance for the same-sign dilepton RPV signal, including top branching fractions, is between 0.25% and 0.5%, comparable to the (0.29 0.04)% quoted by CMS for the SM

t t events [3842].

important evidence for baryon number violation. It is indeed almost impossible to obtain in other realistic new physics scenarios. On the experimental side, a precise measurement of this asymmetry, in which systematic uncertainties cancel, could provide important constraints on our model. In addition, a limit on the production rate of negatively charged

Lepton charge asymmetry in SR0 Lepton charge asymmetry in SR8

1000

200 300 400 500 600 700 800 900 1000

-0.85

-0.87

-0.89

-0.9

-0.89

-0.87

-0.37

-0.83

-0.85

-0.87

-0.86

-0.84

-0.31

-0.066

-0.81

-0.82

-0.83

-0.82

-0.8

-0.24

-0.047

-0.012

-0.78

-0.8

-0.78

-0.77

-0.76

-0.14

-0.041

-0.012

-0.0031

-0.71

-0.7

-0.1

-0.018

-0.01

-0.015

0.0055

-0.7

-0.65

-0.63

-0.038

0.0031

0.011

-0.0055

-0.0026

-9.7e-05

-0.53

-0.023

-0.011

0.0041

0.0011

-0.0012

-0.00042

0.011

-0.1

-0.0027

-0.00051

-0.0066

-0.0026

0.011

0.012

0.017

0.024

-0.84

-0.87

-0.89

900

-0.9

-0.89

-0.87

-0.37

-0.82

-0.85

-0.86

-0.84

-0.31

-0.066

800

-0.8

-0.82

-0.83

-0.81

-0.8

-0.24

-0.047

-0.012

700

M g ~

-0.8

-0.75

-0.14

-0.041

600

M g ~

-0.76

-0.77

-0.012

-0.0032

600

-0.69

-0.71

-0.69

-0.1

-0.018

-0.01

-0.015

0.0058

500

-0.7

-0.63

-0.61

-0.036

0.0042

0.012

-0.0057

-0.0038

-0.00054

400

-0.49

-0.023

-0.012

0.0067

0.0051

-0.00096

-0.00097

0.02

300

-0.1

0.014

0.053

-0.0061

-0.017

0.034

0.022

0.034

0.039

200

200 300 400 500 600 700 800 900 1000 200

Mq~

Figure 10. Lepton charge asymmetry of eq. (1.3) exhibited by the same-sign dilepton RPV signal in SR0 and SR8. The ~dL contributions to the top pair production are not included here.

lepton pairs only, for which SM irreducible backgrounds are smaller, could in principle be used to improve the current bounds in the upper half of the M~q M~g plane.

6 Conclusion

In this paper, we have analyzed in details the same-sign top-quark pair signature of the MSSM in the presence of R-parity violation. To ensure a su ciently long proton lifetime, we enforce the MFV hypothesis, which predicts negligible lepton number violating couplings and specic avor hierarchies for those violating baryon number, IJKUIDJDK. In this

respect, we have considered both the full MFV prediction [5, 6] as well as its holomorphic restriction [9], see table 1. Our main results are the followings:

1. By going through all the possible sparticle decay chains, we showed that the same-sign dilepton signature is a generic feature of the MSSM with R-parity violation. Indeed, independently of the specic MFV implementation, most of the dominant processes lead to same-sign top-quark pairs, because the RPV decays of down-type squarks and gauginos always produce top quarks. By contrast, searches for multijet resonances have a much more restricted reach. Actually, only stop intermediate states have a good probability to lead to nal states made only of light-quark jets (provided ~t t

is kinematically closed).

2. Since the same-sign dilepton signature is to a large extent universal, it can be conveniently simulated using a simplied theoretical framework, thereby avoiding complicated scans over the MSSM parameter space. In practice, it su ces to include only the g g , g d

~di, and d d

JHEP10(2013)068

~di ~dj (i, j = L, R) sparticle production mechanisms, to tune their respective strength by varying the sparticle masses M~q

and M~g, and to allow for the sparticle RPV decay through either t + 2j, t+ 2j

or ~di t+ j, with only light-quark jets in the full MFV case, or with some b jets

in the holomorphic case. A robust estimate of the nal limit range for all possible MSSM mass and mixing parameters is obtained by turning completely on and o the contribution of ~dL.

3. Using this benchmark strategy, we obtained the approximate exclusion regions shown in gure 7 from the current CMS dilepton searches, using either the full or holomorphic MFV hierarchies. The bounds are typically tighter for the latter thanks to the more numerous b-quark jets. In the future, these exclusion regions are expected to creep upwards. Pushing them well beyond the TeV appears di cult though, and would require new dedicated techniques. In this respect, tailored cuts in transverse missing energy /

ET or hadronic activity (HT , jet multiplicity, jet pT , etc.) as well as information from the lepton charge asymmetry could be exploited. It is also worth to keep in mind that the average hadronic activity, and to a lesser extent the average /

ET , increase with sparticle masses. Once the region just above the electroweak scale is cleared, a better sensitivity to the RPV signal could be achievable.

4. It is well known that sparticles could be rather long-lived even when R-parity is violated. Given the strong suppression of the 1IJ, this is especially true for up-type squarks, which could be copiously produced at the LHC. So, we analyzed in details the lifetimes of the squarks, gluino, and to some extent, neutralino and sleptons. We nd that except with the holomorphic MFV hierarchy at small tan , sparticles tend to decay rather quickly, see gure 4. This remains true even when the dominant top-producing channels are kinematically closed. Note that the gaugino lifetimes can always be extended by sending squark masses well beyond the TeV scale since their decays proceed through virtual squarks. But, provided squark masses are not too heavy, no viable R-hadron candidates in the 100 to 1000 GeV mass range are

possible once MFV is imposed and tan [greaterorsimilar] 15.

5. Neither the stop nor the neutralino are playing an important role in our analysis, because quite independently of their masses, they do not signicantly a ect the same-sign top-quark pair production rate. So, given the CMS dilepton bounds, these particles could still be very light. If the stop is the LSP, the best strategy to constrain its mass remains to look for a single or a pair of two-jet resonances that would arise from p p

6. On a more technical side, we claried several points concerning squark and gaugino decay rates in the presence of the baryonic RPV couplings. In particular, we observed that the Majorana nature of the gluino (or neutralino) does not always imply the equality of the processes involving their decays into conjugate nal states. This is shown analytically for the squark four-body decay processes: B(~qL,R q t d s) 6=

B(~qL,R q t

ds) even though B(, ~

0 t d s) = B(, ~

0 t

ds), see appendix A.3.

The reasons for this are the chiral nature of the RPV and gluino couplings, as well

JHEP10(2013)068

t + jets or p p ~t

t + jets. For a neutralino LSP, assuming all the other sparticles are far heavier, the same-sign top-pair signal may still be useful, though the signal strength should be rather suppressed since one has to rely on the electroweak interactions to produce pairs of neutralinos. Note, though, that this would not hold if the neutralino becomes long-lived. In the presence of a large MSSM mass hierarchy, and with very suppressed couplings, the best handle would be the search for the monotop signals [29] produced via s d

t t~

as the width of the latter. At leading order, this e ect appears to be numerically small for (g g t t + jets), whose ratio with (g g ) stays close to the

expected 1/4.

In conclusion, though baryonic R-parity violation may appear as a naughty twist of Nature, requiring us to delve into the intense hadronic activity of proton colliders, the LHC may actually be well up to the challenge. First, most of this hadronic activity should be accompanied with top or anti-top quarks, which can be e ciently identied by both CMS and ATLAS. Second, from a baryon number point-of-view, the LHC is an asymmetric machine since it collides protons. This could prove invaluable to disentangle B-violating e ects from large SM backgrounds. So, even R-parity violating low-scale supersymmetry should not remain unnoticed for long under the onslaught of the future nominal 14 TeV collisions.

Acknowledgments

We would like to thank Sabine Kraml and Fabio Maltoni for discussions and comments. G.D. would like to thank the LPSC, and C.S. the CP3 institute, for their hospitality. G.D. is a Research Fellow of the F.R.S.-FNRS Belgium. This research has been supported in part by the IISN Fundamental interactions, convention 4.4517.08, and by the Belgian IAP Program BELSPO P7/37.

A Decay widths

The decay widths of squarks, gluinos, and neutralinos in the presence of the R-parity violating couplings have been computed in several places, see in particular ref. [3] and references there. Our purposes here are rst to collect (and sometimes correct) the relevant expressions for the two and three body decay processes, (~qI qJ qK) and

(, ~

01 qIqJqK, qI qJ qK). Second, the four-body squark decay ~qA qAqIqJqK and

~qA qAqI qJ qK are analyzed and their rates computed. Though signicantly phase-space

suppressed, hence usually disregarded, these processes become dominant when the cou

plings able to induce the two-body decays are very suppressed. Finally, as a by-product, we also present the slepton and sneutrino four-body decay rates (~

A(~

A) A(A)qIqJqK),

A(~

A) A(A)qI qJ qK), which would be the only open channels if these particles

were the LSP.

A.1 Two-body squark decays

In terms of gauge eigenstates, the two-body decay widths forIR

dJ dK and ~dJR I

JHEP10(2013)068

are (gure 11a)

dJ dK

= M2~uI m2dJ m2dK8M~uA IR, dJ, dK

IJK|2 , (A.1)

~dJR I

= M2~dJ m2uI m2dK8M ~dA

~dJR, uI, dK

IJK|2 , (A.2)

dK) = 0. The standard kinematical function is (a, b, c) = (1, m2b/m2a, m2c/m2a) with (a, b, c)2 = a2 + b2 + c2 2(ab + ac + bc).

These gauge eigenstates mix into mass eigenstates. Introducing the 6 6 mixing

matrices Hf, f = u, d, e, relating the mass eigenstates ~fA, A = 1, . . . , 6 to the gauge eigenstates ( ~fIL, ~fIR), I = 1, 2, 3, the rates become

while (IL

dJ dK) = ( ~dJR I

~dA I

= M2~dJ m2uI m2dK8M ~dA

~dA, uI, dK

ILKHdA(L+3)

2 , (A.3)

= M2~uI m2dJ m2dK8M~uA A, dJ, dK

dJ dK

LJKHuA(L+3)

2 . (A.4)

Under MFV, the four blocks HfIJ, Hf(I+3)(J+3), HfI(J+3) and Hf(I+3)J, I, J = 1, 2, 3, are close to diagonal (exactly diagonal for f = e). When avor mixings are neglected, we dene a separate LR mixing matrix for each squark and slepton avor, so that

JHEP10(2013)068

HfII HfI(I+3)

Hf(I+3)I Hf(I+3)(I+3)

~fi X

fiL

~fL X

fiR

~fR X

(A.5)

For example, when only tds is signicant (and using tds =

tsd), the allowed two-body

decay channels are

~di ts

(13 GeV) |

tds|2

diR

2 , (A.6)

i t

(13 GeV) |

tds|2 | siR|2 , (A.7)

~ti

(18 GeV) |

tds|2

, (A.8)

for squark masses of 450 GeV. Note that under MFV, the LR mixings are tuned by the quark masses, so s,d1R s,d2R 1.

A.2 Three-body gaugino decays

When light, the gluino and lightest neutralino decay predominantly through virtual squark exchanges, see gure 11b. The amplitudes and decay rates in the general case are rather involved, so we introduce a few approximations. First, we keep only one RPV coupling as signicant, and take tds for deniteness. Second, up squarks are considered degenerate in mass, and so are down squarks. From this, the sum over the virtual squark six states simplies thanks to the unitarity of the squark mixing matrices (GIM mechanism). Third, this also implies that the wino contribution cancels out, leaving only the bino and Higgsinos. Since the latter couplings are tuned by the quark Yukawa couplings, we consider only the bino component of ~

01 in the following.

Under these simplications, the decay amplitudes take the form

M t

= gtsd{vPRvt}{sPRvd}+ gstd{vPRvs}{tPRvd}+ gdts{vPRvd}{tPRvs} ,(A.9a)

M(t d s) = gtsd{vPLvt}{sPLvd} + gstd{vPLvs}{tPLvd} + gdts{vPLvd}{tPLvs} ,(A.9b)

u~ d

g ~

d s

~ s

( 1)

a. ( 1)

b. ( 2)

b. ( 3)

~ uI

~ d

~ s

~ d

JHEP10(2013)068

( 2)

( 1)

c. ( 2)

c. ( 3)

Figure 11. The squark two-body (a), gluino three-body (b), and squark four-body decay processes (c) induced by the RPV couplings . For (b) and (c), the diagrams with t d s instead of t ds or with a neutralino instead of a gluino are similar. For the four-body decays, crossed diagrams are understood when q is identical to one of the other quarks in the nal state.

with PL,R = (1 5)/2 and

abc =

tds2gS

cbcccdT cdca (pb + pc)2 M2~a

, g~

abc =

tds YaReN1B

2 cos W

cacbcc

(pb + pc)2 M2~a

, (A.10)

where T ij are SU(3)C generators, is an adjoint color index, ca,b,c,d are fundamental color indices (summation over repeated indices is understood), gS and e are the strong and electromagnetic coupling constants, W is the Weinberg angle, YaR is the weak hypercharge of aR (YtR = 4/3 and YdR = YsR = 2/3), and N1B is the mixing angle between the bino

gauge eigenstate and the lightest neutralino mass eigenstate. Under conjugation g g, it is understood that tds

tds, N1B N1B, and T ij T ji, but Ya and cacbcc stay put.

In eq. (A.10), we set the widths of the squarks to zero in their respective propagators since we are only interested in the situation where they are relatively far o their mass shell.

The squared amplitudes have to be summed over the quark spins and color indices, and averaged over the gaugino spins as well as, and in the gluino case, over the adjoint color index. The sum over the spins can be done using the usual formulas provided some fermion lines are inverted using charge conjugation. Then, the squared amplitudes are the same for t

ds and t d s,

|M ( t d s)|2 = M

= 4|gtsd|2p pt ps pd + 4 Re(gtsdgstd)g(p, pt, ps, pd)

+ 4|gstd|2p ps pt pd4 Re(gtsdgdts)g(p, pt, pd, ps) + 4|gdts|2p pd pt ps+4 Re(gdtsgstd)g(p, pd, ps, pt),(A.11)

with g(a, b, c, d) = (a b)(c d) + (a c)(b d) (a d)(b c). Summation over the color indices

is understood for the gabcgdef coe cients, and can be done using the standard formulas:

ijklmn = det

il im in

jl jm jn

kl km kn

Xa=1T aijT akl = 12 iljk 1 3ijkl

. (A.12)

From the squared amplitudes, the gaugino RPV decay rates are

( t d s) = t

= 1

(2)3

C 32M3

Xspins|M( tds)|2 , (A.13)

with C~01 = 1/2 and C~g = 1/2 1/8 for the spin and color averages. For the neutralino

case, we reproduce the result of ref. [54] once the GIM mechanism is enforced and non-bino contributions discarded. As noted there, this result disagrees with the earlier computation done in ref. [55], in which the interference terms appear to drop out in the massless quark limit (the same holds for ref. [56], quoted in ref. [3]). By contrast, we nd that for both the neutralino and gluino decays, the interference terms survive in that limit.

The phase space measure d tds can be written in terms of the usual Dalitz plot variables m2ab = (pa +pb)2. In the limit where md, ms 0, the integration limits are rather

simple,

d tds =

d tds

JHEP10(2013)068

m2t

dm2ts

(M2 m2ts)(m2tsm2t)/m2ts

0 dm2sd . (A.14)

Even setting mt to zero and taking all squarks degenerate (with mass M~q), the analytic expression for the fully integrated rate is quite complicated. In the M~q/M limit,

both g

abc become momentum independent, and the di erential rates are easily integrated:

( t d s) =

abc and g~

SM~g

M4~g

2562 |

tds|2

M4~q

1 + 12

+ O

M6~g

M6~q

, (A.15a)

01 t d s

= M~

0 |N1B|2

1922 cos2 W |

M4~01

tds|2

M4~q

1 + 1

+ O

M6~01

M6~q

, (A.15b)

where the 1/2 in the nal brackets originate from the interference terms. The fact that both amount to a 50% correction is coincidental.

Note that these expressions are not to be used when the gaugino and squark masses are close, or when the gaugino is not su ciently heavy to justify setting the top-quark mass to zero. In these cases, the phase-space integrals have to be performed numerically (we actually rely on the FeynRulesMadGraph5 software chain [34, 35] for our simulations). For example, taking M = 450 GeV, M~q = 600 GeV, S = 0.1, = 1/128, |N1B| = 1, and

mt = 170 GeV gives

( t d s) = |

tds|2 (3.7 + 1.8) 103 GeV , (A.16)

01 t d s

= |

tds|2 (4.3 + 2.1) 104 GeV , (A.17)

where the rst (second) numbers in the brackets denote the direct (interfering) contributions. For comparison, eq. (A.15) give the slightly larger estimates ( t d s) =

| tds|2 6.6 103 GeV and (~01 t d s) = | tds|2 6.8 104 GeV. Finally, the evolu

tion of the gluino lifetime as a function of its mass as well as that of the virtual squarks is shown in gure 12.

g tds

~ ~

q q+g q+tds

10-24

10-23

10-22

10-21

10-20

10-19

10-18

10-3

10-21

10-1

10-2

10-3

10-4

10-5

10-6

10-7

10-4

10-20

1200

10-5

1200

10-19

10-6

G []

GeV

600

GeV

600

10-7

10-8

10-9

10-10

10-11

10-18

10-17

10-16

10-15

10-14

t []

G []

M = 300

500 1500 2000

1000

500 1000 1500 2000 2500 3000

M [GeV]

Figure 12. Left: the gluino partial decay width and lifetime, for tds = 1, as a function of the virtual squark mass M~q = M~t = M ~d = M~s. The lower (red) curves show the impact of neglecting interference terms: after a slight increase, it quickly settles at its asymptotic value of 3/2. Right: typical four-body squark partial decay rate and lifetime, again for tds = 1 and degenerate squarks, as a function of the virtual gluino mass. This time, interference terms are neglected. The lower (red) curves show the rate for the ID, J D contributions, and the upper (blue) ones the IM, J M

contributions. The much slower decoupling of the latter is due to the additional factor of M~g required for the chirality ip. In both gures, the corresponding rates for neutralinos can be obtained by a simple rescaling, see eqs. (A.15) and (A.20). Finally, the values of the rates when the mass of the virtual squark or gluino is 1 TeV correspond to those quoted in section 3.

A.3 Four-body squark decays

The four-body processes shown in gure 11c are relevant when there is a large avor hierarchy between the RPV couplings. Indeed, when the two-body decay is very suppressed, it becomes advantageous to proceed through a virtual gluino or neutralino which then decays via the largest RPV coupling. Under the same simplifying assumptions as for the gluino and neutralino decays, the amplitudes can be obtained from eq. (A.9) as

M(~qi q q X) =q qi2PL qi1PR

JHEP10(2013)068

2gST cqc~u

p~g + M~g

M ( X) , (A.18a)

M ~qi q ~

01 q X

=q YqRN1B qi2PLYqLN1B qi1PR

e/ 2 cos W

p /~01 + M~01M ~

01 X

(A.18b)

M( X). The two-by-two squark mixing

matrices q are dened in eq. (A.5). Note that for q = d, t, s and X = t d s, one should also include the crossed processes since there are two identical quarks in the nal states. We will ignore this complication in the following.

The calculation of the squared amplitudes, summed over spins and colors, proceeds as before, but the four-body phase-space integral cannot be done analytically. As before, we rely on the FeynRulesMadGraph5 software chain [34, 35] for our simulations. Still, it is interesting to push the analytical study a bit further, and derive the scaling of the decay rates in terms of the gaugino and virtual squark masses. This is not so trivial since the virtual squarks have masses similar to the initial decaying squark, and thus the momentum

where X = t ds or t d s and M( X) = v

dependences of their propagators cannot be neglected. So, to proceed and partly perform the phase-space integrals, we neglect all the interference terms. In the previous section, those were found to increase the gaugino decay rates by 50%, so the present computation should not be expected to hold to better than a factor of about two. The three direct contributions can be integrated recursively, leading to

(~qL q t d s)dir~g

0~g

~qR q t

dir 0~g= ID~q,~t,~g + J D~q,~s,~g + J D~q,~d,~g , (A.19a)

(~qR q t d s)dir~g

0~g

~qL q t

dir 0~g= IM~q,~t,~g + J M~q,~s,~g + J M~q,~d,~g , (A.19b)

(~qL f t d s)dir~

JHEP10(2013)068

~qR f t

dir~01Y 2qR 0~= Y 2uRID~q,~t,~ + Y 2dRJ D~q,~s,~ + Y 2sRJ D~q,~d,~ , (A.19c)

(~qR f t d s)dir~

Y 2qL 0~

~qL f t

dir~01Y 2qL 0~= Y 2uRIM~q,~t,~ + Y 2dRJ M~q,~s,~ + Y 2sRJ M~q,~d,~ , (A.19d)

where Yq is the hypercharge of the quark q (remember that under our approximation, the wino and Higgsinos do not contribute), the overall coe cients are

0~g = 2SM~q

963 |

tds|2 1 103 GeV

Y 2qR 0~

M~q

tds|2

300 GeV , (A.20a)

0~ = 32|N1B|4M~q

10243 cos4 W |

tds|2 3 106 GeV

M~q

tds|2

300 GeV |N1B|4 , (A.20b)

and the dimensionless phase-space integrals can be expressed for mq,d,s = 0 as

(ID~q,~t,

IM~q,~t,

M2~q

m2t

dT 2

M2~q

(T mt)2

dT 2~t

M2~q

T 2~t

M2~qT 2 2

T 2T 2~t+m2t

T 2, T 2~t, m2t

T 2

T 4

T 2~tM2~t 2 T2

(A.21)

(J D~q,a,

J M~q,a,

M2~q

m2t

dT 2

M2~q

T 2

m2t

dT 2a

M2~q

T 2a m2t

2 M2~q T 2 2 T2 T 2a

T 2

, (A.22)

and (a, b, c)2 = a2 + b2 + c2 2(ab + ac + bc). The subscript dir serves as a reminder

that interference terms originating from crossed processes when q = t, d, s, X = t d s and from squaring the amplitude are both neglected. Decay rates into mass eigenstates are found using eq. (A.5).

These expressions remain valid if the gluino or the squark in the decay chain can be on-shell, provided their widths are introduced in the denominators of I and J . In

this respect, it is interesting to note that while B( t d s) = B( t

ds), we nd

T 2aT 4 (T 2a M2a)2 T 2 M2

ds) because ID 6= IM and J D 6= J M. This

di erence can be traced back to the chiral nature of the gaugino-squark-quark and RPV couplings. The projectors in eq. (A.18) leave only either the /

p or the M term of the

that B(~qL,R q t d s) 6= B(~qL,R q t

gaugino propagator to contribute. Because of this, the naive expectation based on the narrow-width approximation should not always be trusted [32] (see also ref. [33, 57]). Numerically, the di erence is negligible over most of the 0 < M < M~q range when the gaugino width is small, but gets maximal in the deep virtual (massless) limits: J D/J M

0 () when M (0).

Specically, setting all squark masses to a common value M~q, the phase-space integrals of each type are identical when mt 0. When M 0, independently of its width,

ID~q,~t, M

0 = J D~q,~s,

M 0 = J D~q,~d, M

0 =

79 82

4 0.011 , (A.23)

IM~q,~t, M

0 = J M~q,~s,

M 0 = J M~q,~d, M

0 = 0 . (A.24)

At the threshold M = M~q, the mass-dependent contribution slightly surpasses that of the direct contribution,

ID~q,~t, M

M~q = J D~q,~s,

M M~q = J D~q,~d, M

M~q =

10 2

2 0.065 , (A.25)

IM~q,~t, M

M M~q = J M~q,~d, M

M~q =

JHEP10(2013)068

M~q = J M~q,~s,

42 39

6 0.080 , (A.26)

while moving into the virtual gaugino regime, the direct contribution rapidly decouples, as can be see expanding the integrals in powers of M~q/M (see gure 12):

ID~q,~t, M

= J D~q,~s,

M = J D~q,~d, M

79 82

M4~q

+ O

M6~q

, (A.27)

IM~q,~t, M

= J M~q,~s,

M = J M~q,~d, M

152148 9

M2~q

+ 7982

M4~q

M6~q

(A.28)

Numerically, 7982 152148 1/23, so the phase-space integrals are very suppressed

when the gaugino gets much heavier than the squarks. In that case, the ~qR q t d s and ~qL q t

ds decay channels dominate. For our purpose, this means that same sign top quarks also arise from these four-body processes, for example via u u LL tt+ 6j or u u RR t t + 6j.

The expressions for the neutralino-induced processes ~

L,R X and ~

L X with

X = t ds or t d s are trivially obtained from eq. (A.18) and eq. (A.19) by replacing the quark hypercharges by the adequate lepton ones, YqL,R YL,R and YqL YL. In this case though, the initial state needs not have a mass close to the virtual squarks. The whole amplitude can be expanded as a series in M~q,~ before performing the phase-space

integration, giving for mt = 0 (very similar expressions were obtained in ref. [13] for the

d decay rate induced by the ud coupling)

~L t d s

~ 01

~R t ds

~ 01

= Y 2uR + 2Y 2dR720

M4~ M4~

M4~

M4~q

1 + 1

, (A.29)

Y 2L 0~

Y 2R 0~

~R t d s

~ 01

~L t ds

~ 01

= Y 2uR + 2Y 2dR360

M2~ M2~

1 + M2~ M2~

M4~

M4~q

1 + 12

Y 2R 0~

Y 2L 0~

(A.30)

where the 1/2 originate from the interference terms (as in eq. (A.15)), Y 2uR + 2Y 2dR = 8/3, YL = 1, YR = 2, and (

L X)~

01 = (~

L X)~

01 since YL = YL and YR = 0.

Open Access. This article is distributed under the terms of the Creative Commons Attribution License which permits any use, distribution and reproduction in any medium, provided the original author(s) and source are credited.

References

[1] https://twiki.cern.ch/twiki/bin/view/AtlasPublic/SupersymmetryPublicResults

Web End =https://twiki.cern.ch/twiki/bin/view/AtlasPublic/SupersymmetryPublicResults .

[2] https://twiki.cern.ch/twiki/bin/view/CMSPublic/PhysicsResultsSUS

Web End =https://twiki.cern.ch/twiki/bin/view/CMSPublic/PhysicsResultsSUS .

[3] R. Barbier et al., R-parity violating supersymmetry, http://dx.doi.org/10.1016/j.physrep.2005.08.006

Web End =Phys. Rept. 420 (2005) 1 [http://arxiv.org/abs/hep-ph/0406039

Web End =hep-ph/0406039 ] [http://inspirehep.net/search?p=find+EPRINT+hep-ph/0406039

Web End =INSPIRE ].

[4] Particle Data Group collaboration, J. Beringer et al., Review of Particle Physics (RPP), http://dx.doi.org/10.1103/PhysRevD.86.010001

Web End =Phys. Rev. D 86 (2012) 010001 [http://inspirehep.net/search?p=find+J+Phys.Rev.,D86,010001

Web End =INSPIRE ].

[5] E. Nikolidakis and C. Smith, Minimal Flavor Violation, Seesaw and R-parity, http://dx.doi.org/10.1103/PhysRevD.77.015021

Web End =Phys. Rev. D 77 (2008) 015021 [arXiv:0710.3129] [http://inspirehep.net/search?p=find+EPRINT+arXiv:0710.3129

Web End =INSPIRE ].

[6] C. Smith, Proton stability from a fourth family, http://dx.doi.org/10.1103/PhysRevD.85.036005

Web End =Phys. Rev. D 85 (2012) 036005 [arXiv:1105.1723] [http://inspirehep.net/search?p=find+EPRINT+arXiv:1105.1723

Web End =INSPIRE ].

[7] L. Hall and L. Randall, Weak scale e ective supersymmetry, http://dx.doi.org/10.1103/PhysRevLett.65.2939

Web End =Phys. Rev. Lett. 65 (1990) 2939 [ http://inspirehep.net/search?p=find+J+Phys.Rev.Lett.,65,2939

Web End =INSPIRE ].

[8] G. DAmbrosio, G. Giudice, G. Isidori and A. Strumia, Minimal avor violation: An e ective eld theory approach, http://dx.doi.org/10.1016/S0550-3213(02)00836-2

Web End =Nucl. Phys. B 645 (2002) 155 [http://arxiv.org/abs/hep-ph/0207036

Web End =hep-ph/0207036 ] [http://inspirehep.net/search?p=find+J+Nucl.Phys.,B645,155

Web End =INSPIRE ].

[9] C. Cski, Y. Grossman and B. Heidenreich, MFV SUSY: A Natural Theory for R-Parity Violation, http://dx.doi.org/10.1103/PhysRevD.85.095009

Web End =Phys. Rev. D 85 (2012) 095009 [arXiv:1111.1239] [http://inspirehep.net/search?p=find+EPRINT+arXiv:1111.1239

Web End =INSPIRE ].

[10] G. Krnjaic and D. Stolarski, Gauging the Way to MFV, http://dx.doi.org/10.1007/JHEP04(2013)064

Web End =JHEP JHEP04 (2013) 064 [arXiv:1212.4860] [http://inspirehep.net/search?p=find+EPRINT+arXiv:1212.4860

Web End =INSPIRE ].

[11] R. Franceschini and R. Mohapatra, New Patterns of Natural R-Parity Violation with Supersymmetric Gauged Flavor, http://dx.doi.org/10.1007/JHEP04(2013)098

Web End =JHEP 04 (2013) 098 [arXiv:1301.3637] [http://inspirehep.net/search?p=find+EPRINT+arXiv:1301.3637

Web End =INSPIRE ].

[12] C. Cski and B. Heidenreich, A Complete Model for R-parity Violation, arXiv:1302.0004 [http://inspirehep.net/search?p=find+EPRINT+arXiv:1302.0004

Web End =INSPIRE ].

[13] B. Allanach, A. Dedes and H. Dreiner, R parity violating minimal supergravity model, http://dx.doi.org/10.1103/PhysRevD.69.115002

Web End =Phys. Rev. D 69 (2004) 115002 [Erratum ibid. D 72 (2005) 079902] [http://arxiv.org/abs/hep-ph/0309196

Web End =hep-ph/0309196 ] [http://inspirehep.net/search?p=find+EPRINT+hep-ph/0309196

Web End =INSPIRE ].

JHEP10(2013)068

[14] G. Durieux, J.-M. Gerard, F. Maltoni and C. Smith, Three-generation baryon and lepton number violation at the LHC, http://dx.doi.org/10.1016/j.physletb.2013.02.052

Web End =Phys. Lett. B 721 (2013) 82 [arXiv:1210.6598] [http://inspirehep.net/search?p=find+EPRINT+arXiv:1210.6598

Web End =INSPIRE ].

[15] B. Allanach and B. Gripaios, Hide and Seek With Natural Supersymmetry at the LHC, http://dx.doi.org/10.1007/JHEP05(2012)062

Web End =JHEP 05 (2012) 062 [arXiv:1202.6616] [http://inspirehep.net/search?p=find+EPRINT+arXiv:1202.6616

Web End =INSPIRE ].

[16] M. Asano, K. Rolbiecki and K. Sakurai, Can R-parity violation hide vanilla supersymmetry at the LHC?, http://dx.doi.org/10.1007/JHEP01(2013)128

Web End =JHEP 01 (2013) 128 [arXiv:1209.5778] [http://inspirehep.net/search?p=find+EPRINT+arXiv:1209.5778

Web End =INSPIRE ].

[17] J. Berger, M. Perelstein, M. Saelim and P. Tanedo, The Same-Sign Dilepton Signature of RPV/MFV SUSY, http://dx.doi.org/10.1007/JHEP04(2013)077

Web End =JHEP 04 (2013) 077 [arXiv:1302.2146] [http://inspirehep.net/search?p=find+EPRINT+arXiv:1302.2146

Web End =INSPIRE ].

[18] D. Choudhury, M. Datta and M. Maity, Search for the lightest scalar top quark in R-parity violating decays at the LHC, http://dx.doi.org/10.1007/JHEP10(2011)004

Web End =JHEP 10 (2011) 004 [arXiv:1106.5114] [http://inspirehep.net/search?p=find+EPRINT+arXiv:1106.5114

Web End =INSPIRE ].

[19] J.A. Evans and Y. Kats, LHC Coverage of RPV MSSM with Light Stops, http://dx.doi.org/10.1007/JHEP04(2013)028

Web End =JHEP 04 (2013) 028 [arXiv:1209.0764] [http://inspirehep.net/search?p=find+EPRINT+arXiv:1209.0764

Web End =INSPIRE ].

[20] Z. Han, A. Katz, M. Son and B. Tweedie, Boosting Searches for Natural SUSY with RPV via Gluino Cascades, http://dx.doi.org/10.1103/PhysRevD.87.075003

Web End =Phys. Rev. D 87 (2013) 075003 [arXiv:1211.4025] [http://inspirehep.net/search?p=find+EPRINT+arXiv:1211.4025

Web End =INSPIRE ].

[21] R. Franceschini and R. Torre, RPV stops bump o the background,

http://dx.doi.org/10.1140/epjc/s10052-013-2422-x

Web End =Eur. Phys. J. C 73 (2013) 2422 [arXiv:1212.3622] [http://inspirehep.net/search?p=find+EPRINT+arXiv:1212.3622

Web End =INSPIRE ].

[22] CMS collaboration, Search for three-jet resonances in pp collisions at s = 7 TeV, http://dx.doi.org/10.1016/j.physletb.2012.10.048

Web End =Phys. Lett. B 718 (2012) 329 [arXiv:1208.2931] [http://inspirehep.net/search?p=find+EPRINT+arXiv:1208.2931

Web End =INSPIRE ].

[23] ATLAS collaboration, Search for pair production of massive particles decaying into three quarks with the ATLAS detector in s = 7 TeV pp collisions at the LHC,http://dx.doi.org/10.1007/JHEP12(2012)086

Web End =JHEP 12 (2012) 086 [arXiv:1210.4813] [http://inspirehep.net/search?p=find+EPRINT+arXiv:1210.4813

Web End =INSPIRE ].

[24] M. Fairbairn, A. Kraan, D. Milstead, T. Sjstrand, P.Z. Skands and T. Sloan, Stable massive particles at colliders, http://dx.doi.org/10.1016/j.physrep.2006.10.002

Web End =Phys. Rept. 438 (2007) 1 [http://arxiv.org/abs/hep-ph/0611040

Web End =hep-ph/0611040 ] [http://inspirehep.net/search?p=find+EPRINT+hep-ph/0611040

Web End =INSPIRE ].

[25] ATLAS collaboration, Searches for Heavy Long-Lived Sleptons and R-hadrons with the ATLAS detector in pp collisions at s = 7 TeV, http://cds.cern.ch/record/1460272

Web End =ATLAS-CONF-2012-075 (2012).

[26] N. Arkani-Hamed and S. Dimopoulos, Supersymmetric unication without low energy supersymmetry and signatures for ne-tuning at the LHC, http://dx.doi.org/10.1088/1126-6708/2005/06/073

Web End =JHEP 06 (2005) 073 [http://arxiv.org/abs/hep-th/0405159

Web End =hep-th/0405159 ] [http://inspirehep.net/search?p=find+EPRINT+hep-th/0405159

Web End =INSPIRE ].

[27] G. Giudice and A. Romanino, Split supersymmetry, http://dx.doi.org/10.1016/j.nuclphysb.2004.11.048

Web End =Nucl. Phys. B 699 (2004) 65 [Erratum ibid. B 706 (2005) 65-89] [http://arxiv.org/abs/hep-ph/0406088

Web End =hep-ph/0406088 ] [http://inspirehep.net/search?p=find+EPRINT+hep-ph/0406088

Web End =INSPIRE ].

[28] M. Buchkremer and A. Schmidt, Long-lived heavy quarks: a review,

http://dx.doi.org/10.1155/2013/690254

Web End =Adv. High Energy Phys. 2013 (2013) 690254 [arXiv:1210.6369] [http://inspirehep.net/search?p=find+EPRINT+arXiv:1210.6369

Web End =INSPIRE ].

[29] J. Andrea, B. Fuks and F. Maltoni, Monotops at the LHC, http://dx.doi.org/10.1103/PhysRevD.84.074025

Web End =Phys. Rev. D 84 (2011) 074025 [arXiv:1106.6199] [http://inspirehep.net/search?p=find+EPRINT+arXiv:1106.6199

Web End =INSPIRE ].

[30] G. Colangelo, E. Nikolidakis and C. Smith, Supersymmetric models with minimal avour violation and their running, http://dx.doi.org/10.1140/epjc/s10052-008-0796-y

Web End =Eur. Phys. J. C 59 (2009) 75 [arXiv:0807.0801] [http://inspirehep.net/search?p=find+EPRINT+arXiv:0807.0801

Web End =INSPIRE ].

[31] A. Arbey, M. Battaglia, A. Djouadi, F. Mahmoudi and J. Quevillon, Implications of a125 GeV Higgs for supersymmetric models, http://dx.doi.org/10.1016/j.physletb.2012.01.053

Web End =Phys. Lett. B 708 (2012) 162 [arXiv:1112.3028] [http://inspirehep.net/search?p=find+EPRINT+arXiv:1112.3028

Web End =INSPIRE ].

[32] D. Berdine, N. Kauer and D. Rainwater, Breakdown of the Narrow Width Approximation for New Physics, http://dx.doi.org/10.1103/PhysRevLett.99.111601

Web End =Phys. Rev. Lett. 99 (2007) 111601 [http://arxiv.org/abs/hep-ph/0703058

Web End =hep-ph/0703058 ] [http://inspirehep.net/search?p=find+EPRINT+hep-ph/0703058

Web End =INSPIRE ].

JHEP10(2013)068

[33] S. Choi, M. Drees, A. Freitas and P. Zerwas, Testing the Majorana Nature of Gluinos and Neutralinos, http://dx.doi.org/10.1103/PhysRevD.78.095007

Web End =Phys. Rev. D 78 (2008) 095007 [arXiv:0808.2410] [http://inspirehep.net/search?p=find+EPRINT+arXiv:0808.2410

Web End =INSPIRE ].

[34] N.D. Christensen and C. Duhr, FeynRules - Feynman rules made easy, http://dx.doi.org/10.1016/j.cpc.2009.02.018

Web End =Comput. Phys. Commun. 180 (2009) 1614 [arXiv:0806.4194] [http://inspirehep.net/search?p=find+EPRINT+arXiv:0806.4194

Web End =INSPIRE ].

[35] J. Alwall, M. Herquet, F. Maltoni, O. Mattelaer and T. Stelzer, MadGraph 5: Going Beyond, http://dx.doi.org/10.1007/JHEP06(2011)128

Web End =JHEP 06 (2011) 128 [arXiv:1106.0522] [http://inspirehep.net/search?p=find+EPRINT+arXiv:1106.0522

Web End =INSPIRE ].

[36] M. Kramer et al., Supersymmetry production cross sections in pp collisions at s = 7 TeV, arXiv:1206.2892 [http://inspirehep.net/search?p=find+EPRINT+arXiv:1206.2892

Web End =INSPIRE ].

[37] https://twiki.cern.ch/twiki/bin/view/LHCPhysics/SUSYCross sections

Web End =https://twiki.cern.ch/twiki/bin/view/LHCPhysics/SUSYCross sections .

[38] CMS collaboration, Search for new physics in events with same-sign dileptons and b-tagged jets in pp collisions at s = 7 TeV, http://dx.doi.org/10.1007/JHEP08(2012)110

Web End =JHEP 08 (2012) 110 [arXiv:1205.3933] [http://inspirehep.net/search?p=find+EPRINT+arXiv:1205.3933

Web End =INSPIRE ].

[39] CMS collaboration, Search for new physics in events with same-sign dileptons and b jets in pp collisions at s = 8 TeV, http://dx.doi.org/10.1007/JHEP03(2013)037

Web End =JHEP 03 (2013) 037 [Erratum ibid. 1307 (2013) 041] [arXiv:1212.6194] [http://inspirehep.net/search?p=find+EPRINT+arXiv:1212.6194

Web End =INSPIRE ].

[40] CMS collaboration, Search for supersymmetry in events with same-sign dileptons, http://cds.cern.ch/record/1459811

Web End =CMS-PAS-SUS-12-017 .

[41] CMS collaboration, Search for supersymmetry in events with same-sign dileptons and b-tagged jets with 8 TeV data, http://cds.cern.ch/record/1494592

Web End =CMS-PAS-SUS-12-029 .

[42] CMS collaboration, Search for new physics with same-sign isolated dilepton events with jets and missing transverse energy, http://dx.doi.org/10.1103/PhysRevLett.109.071803

Web End =Phys. Rev. Lett. 109 (2012) 071803 [arXiv:1205.6615] [http://inspirehep.net/search?p=find+EPRINT+arXiv:1205.6615

Web End =INSPIRE ].

[43] ATLAS collaboration, Search for gluinos in events with two same-sign leptons, jets and missing transverse momentum with the ATLAS detector in pp collisions at s = 7 TeV, http://dx.doi.org/10.1103/PhysRevLett.108.241802

Web End =Phys. Rev. Lett. 108 (2012) 241802 [arXiv:1203.5763] [http://inspirehep.net/search?p=find+EPRINT+arXiv:1203.5763

Web End =INSPIRE ].

[44] ATLAS collaboration, Search for anomalous production of prompt like-sign lepton pairs at s = 7 TeV with the ATLAS detector, http://dx.doi.org/10.1007/JHEP12(2012)007

Web End =JHEP 12 (2012) 007 [arXiv:1210.4538] [http://inspirehep.net/search?p=find+EPRINT+arXiv:1210.4538

Web End =INSPIRE ].

[45] ATLAS collaboration, Search for Supersymmetry in nal states with two same-sign leptons, jets and missing transverse momentum with the ATLAS detector in pp collisions ats = 8 TeV, http://cds.cern.ch/record/1472674

Web End =ATLAS-CONF-2012-105 (2012).

[46] ATLAS collaboration, Search for strongly produced superpartners in nal states with two same sign leptons with the ATLAS detector using 21 fb-1 of proton-proton collisions at s = 8 TeV., http://cds.cern.ch/record/1522430

Web End =ATLAS-CONF-2013-007 (2013).

[47] ATLAS collaboration, Search for anomalous production of events with same-sign dileptons and b jets in 14.3 fb1 of pp collisions at s = 8 TeV with the ATLAS detector, http://cds.cern.ch/record/1547567

Web End =ATLAS-CONF-2013-051 (2013).

[48] J.M. Campbell and R.K. Ellis, ttW + production and decay at NLO, http://dx.doi.org/10.1007/JHEP07(2012)052

Web End =JHEP 07 (2012) 052 [arXiv:1204.5678] [http://inspirehep.net/search?p=find+EPRINT+arXiv:1204.5678

Web End =INSPIRE ].

[49] A. Kardos, Z. Trcsnyi and C. Papadopoulos, Top quark pair production in association with a Z-boson at NLO accuracy, http://dx.doi.org/10.1103/PhysRevD.85.054015

Web End =Phys. Rev. D 85 (2012) 054015 [arXiv:1111.0610] [http://inspirehep.net/search?p=find+EPRINT+arXiv:1111.0610

Web End =INSPIRE ].

[50] M. Garzelli, A. Kardos, C. Papadopoulos and Z. Trcsnyi, Z0-boson production in association with a top anti-top pair at NLO accuracy with parton shower e ects, http://dx.doi.org/10.1103/PhysRevD.85.074022

Web End =Phys. Rev. D 85 (2012) 074022 [arXiv:1111.1444] [http://inspirehep.net/search?p=find+EPRINT+arXiv:1111.1444

Web End =INSPIRE ].

JHEP10(2013)068

[51] J. Thaler and L.-T. Wang, Strategies to Identify Boosted Tops, http://dx.doi.org/10.1088/1126-6708/2008/07/092

Web End =JHEP 07 (2008) 092 [arXiv:0806.0023] [http://inspirehep.net/search?p=find+EPRINT+arXiv:0806.0023

Web End =INSPIRE ].

[52] K. Rehermann and B. Tweedie, E cient Identication of Boosted Semileptonic Top Quarks at the LHC, http://dx.doi.org/10.1007/JHEP03(2011)059

Web End =JHEP 03 (2011) 059 [arXiv:1007.2221] [http://inspirehep.net/search?p=find+EPRINT+arXiv:1007.2221

Web End =INSPIRE ].

[53] T. Plehn, M. Spannowsky and M. Takeuchi, Boosted Semileptonic Tops in Stop Decays, http://dx.doi.org/10.1007/JHEP05(2011)135

Web End =JHEP 05 (2011) 135 [arXiv:1102.0557] [http://inspirehep.net/search?p=find+EPRINT+arXiv:1102.0557

Web End =INSPIRE ].

[54] E.A. Baltz and P. Gondolo, Neutralino decay rates with explicit R-parity violation, http://dx.doi.org/10.1103/PhysRevD.57.2969

Web End =Phys. Rev. D 57 (1998) 2969 [http://arxiv.org/abs/hep-ph/9709445

Web End =hep-ph/9709445 ] [http://inspirehep.net/search?p=find+EPRINT+hep-ph/9709445

Web End =INSPIRE ].

[55] J. Butterworth and H.K. Dreiner, R-parity violation at HERA, http://dx.doi.org/10.1016/0550-3213(93)90334-L

Web End =Nucl. Phys. B 397 (1993) 3 [http://arxiv.org/abs/hep-ph/9211204

Web End =hep-ph/9211204 ] [http://inspirehep.net/search?p=find+EPRINT+hep-ph/9211204

Web End =INSPIRE ].

[56] H.K. Dreiner, P. Richardson and M.H. Seymour, Parton shower simulations of R-parity violating supersymmetric models, http://dx.doi.org/10.1088/1126-6708/2000/04/008

Web End =JHEP 04 (2000) 008 [http://arxiv.org/abs/hep-ph/9912407

Web End =hep-ph/9912407 ] [http://inspirehep.net/search?p=find+EPRINT+hep-ph/9912407

Web End =INSPIRE ].

[57] M. Kramer, E. Popenda, M. Spira and P. Zerwas, Gluino Polarization at the LHC, http://dx.doi.org/10.1103/PhysRevD.80.055002

Web End =Phys. Rev. D 80 (2009) 055002 [arXiv:0902.3795] [http://inspirehep.net/search?p=find+EPRINT+arXiv:0902.3795

Web End =INSPIRE ].

JHEP10(2013)068

Word count: 17967

Show less

SISSA, Trieste, Italy 2013

Abstract

Translate

Baryonic R-parity violation could explain why low-scale supersymmetry has not yet been discovered at colliders: sparticles would be hidden in the intense hadronic activity. However, if the known flavor structures are any guide, the largest baryon number violating couplings are those involving the top/stop, so a copious production of same-sign top-quark pairs is in principle possible. Such a signal, with its low irreducible background and efficient identification through same-sign dileptons, provides us with tell-tale signs of baryon number violating supersymmetry. Interestingly, this statement is mostly independent of the details of the supersymmetric mass spectrum. So, in this paper, after analyzing the sparticle decay chains and lifetimes, we formulate a simplified benchmark strategy that covers most supersymmetric scenarios. We then use this information to interpret the samesign dilepton searches of CMS, draw approximate bounds on the gluino and squark masses, and extrapolate the reach of the future 14 TeV runs.

Details

Title

The same-sign top signature of R-parity violation

Author

Durieux, Gauthier; Smith, Christopher

Pages

1-36

Publication year

2013

Publication date

Oct 2013

Publisher

Springer Nature B.V.

e-ISSN

10298479

Source type

Scholarly Journal

Language of publication

English

DOI

https://doi.org/10.1007/JHEP10(2013)068

ProQuest document ID

1652924810

SISSA, Trieste, Italy 2013

The same-sign top signature of R-parity violation

Jump to:

Full Text

Abstract

Details

Suggested sources