Observation of a New Excited Beauty Strange Baryon Decaying to Xi(-)(b)pi(+)pi(-)

Abstract

The Ξ− b πþπ− invariant mass spectrum is investigated with an event sample of proton-proton collisions at ffiffi s p ¼ 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 Ξbð6100Þ−, is observed at a Ξ− b πþπ− invariant mass of 6100.3 0.2ðstatÞ 0.1ðsystÞ 0.6ðΞ− b Þ MeV, where the last uncertainty reflects the precision of the Ξ− b baryon mass. The upper limit on the Ξbð6100Þ− natural width is determined to be 1.9 MeV at 95% confidence level. The low Ξbð6100Þ− 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 Ξc baryon states, the new Ξbð6100Þ− resonance and its decay sequence are consistent with the orbitally excited Ξ− b baryon, with spin and parity quantum numbers JP ¼ 3=2−.