Charm fragmentation fractions and cc¯ cross section in p–Pb collisions at sNN=5.02TeV

Abstract

The total charm-quark production cross section per unit of rapidity $\text{d}\sigma (\text{c}\overline{\text{c}})/\text{d}y$, and the fragmentation fractions of charm quarks to different charm-hadron species $f(\text{c}\to {\text{h}}_{\text{c}})$, are measured for the first time in p–Pb collisions at $\sqrt{s_{\text{NN}}}=5.02\text{Te}\text{V}$ at midrapidity ($-0.96<y<0.04$ in the centre-of-mass frame) using data collected by ALICE at the CERN LHC. The results are obtained based on all the available measurements of prompt production of ground-state charm-hadron species: ${\text{D}}^0$, ${\text{D}}^{+}$, ${\text{D}}_{\text{s}}^{+}$, and $\mathrm{J}/\psi$ mesons, and ${\mathrm{\Lambda }}_{\text{c}}^{+}$ and ${\mathrm{\Xi }}_{\text{c}}^0$ baryons. The resulting cross section is $\text{d}\sigma (\text{c}\overline{\text{c}})/\text{d}y=219.6\pm 6.3(\mathrm{stat}.)_{-11.8}^{+10.5}(\mathrm{syst}.)_{-2.9}^{+8.3}(\mathrm{extr}.)\pm 5.4(\text{BR})\pm 4.6(\mathrm{lumi}.)\pm 19.5(\text{rapidity shape})+15.0({\mathrm{\Omega }}_{\text{c}}^0)\text{mb}$, which is consistent with a binary scaling of pQCD calculations from pp collisions. The measured fragmentation fractions are compatible with those measured in pp collisions at $\sqrt{s}=5.02$ and 13 TeV, showing an increase in the relative production rates of charm baryons with respect to charm mesons in pp and p–Pb collisions compared with ${\mathrm{e}}^{+}{\mathrm{e}}^{-}$ and ${\mathrm{e}}^{-}\mathrm{p}$ collisions. The $p_{\text{T}}$-integrated nuclear modification factor of charm quarks, $R_{\text{pPb}}(\text{c}\overline{\text{c}})=0.91\pm 0.04{(\mathrm{stat}.)}_{-0.09}^{+0.08}{(\mathrm{syst}.)}_{-0.03}^{+0.05}(\mathrm{extr}.)\pm 0.03(\mathrm{lumi}.)$, is found to be consistent with unity and with theoretical predictions including nuclear modifications of the parton distribution functions.