Abstract
The Ξ_{b}^{-}π^{+}π^{-} invariant mass spectrum is investigated with an event sample of proton-proton collisions at sqrt[s]=13 TeV, collected by the CMS experiment at the LHC in 2016-2018 and corresponding to an integrated luminosity of 140 fb^{-1}. The ground state Ξ_{b}^{-} is reconstructed via its decays to J/ψΞ^{-} and J/ψΛK^{-}. A narrow resonance, labeled Ξ_{b}(6100)^{-}, is observed at a Ξ_{b}^{-}π^{+}π^{-} invariant mass of 6100.3±0.2(stat)±0.1(syst)±0.6(Ξ_{b}^{-}) MeV, where the last uncertainty reflects the precision of the Ξ_{b}^{-} baryon mass. The upper limit on the Ξ_{b}(6100)^{-} natural width is determined to be 1.9 MeV at 95%confidence level. The low Ξ_{b}(6100)^{-} signal yield observed in data does not allow a measurement of the quantum numbers of the new state. However, following analogies with the established excited Ξ_{c} baryon states, the new Ξ_{b}(6100)^{-} resonance and its decay sequence are consistent with the orbitally excited Ξ_{b}^{-} baryon, with spin and parity quantum numbers J^{P}=3/2^{-}.
Highlights
The Ξb baryon family consists of isodoublet states composed of bsq quarks, where q represents an up or a down quark for the Ξ0b and Ξ−b states, respectively
Various theoretical models and calculations predict a spectrum of excited Ξb baryons [2,3,4,5,6,7,8,9,10,11,12,13,14,15,16]
The inclusion of charge-conjugated states is implied throughout this Letter
Summary
859 Æ 36 and 815 Æ 74 for the Ξ−b → J=ψΞ− and fully reconstructed Ξ−b → J=ψΛK− decay modes, respectively, with the uncertainties being statistical only. The fitted Ξ−b masses of 5797.0 Æ 0.7 and 5800.1 Æ 1.2 MeV, respectively for the J=ψΞ− and J=ψΛK− channels, the uncertainties being statistical only, are consistent with each other and with the world-average value, 5797.0 Æ 0.6 MeV [20]. The. 5.63 < MðJ=ψΛK−Þ < 5.76 GeV mass region is used for the partially reconstructed Ξ−b → J=ψΣ0K− decay mode, shown by the dashed vertical lines in Fig. 2 (lower). 5.63 < MðJ=ψΛK−Þ < 5.76 GeV mass region is used for the partially reconstructed Ξ−b → J=ψΣ0K− decay mode, shown by the dashed vertical lines in Fig. 2 (lower) These mass ranges are selected through the same optimization procedure as used for the other selection criteria. The largest deviations in the measured mass are 0.01 and 0.04 MeV, respectively, for the variations of the signal and background models; these values are taken as the two corresponding systematic uncertainties
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