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CMS-BPH-12-001 ; CERN-PH-EP-2012-118
Observation of a New Ξb Baryon
Phys. Rev. Lett. 108 (2012) 252002
Abstract: The observation of a new b baryon via its strong decay into Ξbπ+ (plus charge conjugates) is reported. The measurement uses a data sample of pp collisions at s = 7 TeV collected by the CMS experiment at the LHC, corresponding to an integrated luminosity of 5.3 inverse femtobarns. The known Ξb baryon is reconstructed via the decay chain ΞbJ/ψΞμ+μΛ0π, with Λ0pπ. A peak is observed in the distribution of the difference between the mass of the Ξbπ+ system and the sum of the masses of the Ξb and π+, with a significance exceeding five 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 Ξb.
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