Physical Review Letters, vol.108, no.25, 2012 (SCI-Expanded)
The observation of a new b baryon via its strong decay into Ξb-π + (plus charge conjugates) is reported. The measurement uses a data sample of pp collisions at √s=7TeV collected by the CMS experiment at the LHC, corresponding to an integrated luminosity of 5.3fb -1. The known Ξb- baryon is reconstructed via the decay chain Ξb-→J/ψΞ -→μ +μ -Λ0π -, with Λ0→pπ -. A peak is observed in the distribution of the difference between the mass of the Ξb-π + system and the sum of the masses of the Ξb- and π +, with a significance exceeding 5 standard deviations. The mass difference of the peak is 14.84±0.74(stat)±0.28(syst)MeV. The new state most likely corresponds to the JP=3/2 + companion of the Ξ b. © 2012 CERN.