Observation of new excited Bs0 states

Abstract

A structure is observed in the $B^{\pm }{K}^{\mp }$ mass spectrum in a sample of proton–proton collisions at centre-of-mass energies of 7, 8, and 13 TeV, collected with the LHCb detector and corresponding to a total integrated luminosity of 9${\text{fb}}^{-1}$. The structure is interpreted as the result of overlapping excited $B_s^0$ states. With high significance, a two-peak hypothesis provides a better description of the data than a single resonance. Under this hypothesis the masses and widths of the two states, assuming they decay directly to $B^{\pm }{K}^{\mp }$, are determined to be $$\begin{array}{cc}\hfill m_1& =6063.5\pm 1.2\text{(stat)}\pm 0.8\text{(syst)}\text{Me},\hfill \\ \hfill {\mathrm{\Gamma }}_1& =26\pm 4\text{(stat)}\pm 4\text{(syst)}\text{Me},\hfill \\ \hfill m_2& =6114\pm 3\text{(stat)}\pm 5\text{(syst)}\text{Me},\hfill \\ \hfill {\mathrm{\Gamma }}_2& =66\pm 18\text{(stat)}\pm 21\text{(syst)}\text{Me}.\hfill \end{array}$$Alternative values assuming a decay through $B^{\ast \pm }{K}^{\mp }$, with a missing photon from the $B^{\ast \pm }\to B^{\pm }\gamma$ decay, which are shifted by approximately 45$\text{Me}$V, are also determined. The possibility of a single state decaying in both channels is also considered. The ratio of the total production cross-section times branching fraction of the new states relative to the previously observed $B_{s2}^{\ast 0}$ state is determined to be $0.87\pm 0.15\text{(stat)}\pm 0.19\text{(syst)}$.