Thursday, Oct 18, 2012, 16:30
WHGA/001
V. Chiochia, University of Zurich
Abstract:
The first observation of a new b baryon via its strong decay into Xi(b)^- pi^+ (plus
charge conjugates) is reported. The measurement uses a data sample of pp collisions
at sqrt(s) = 7 TeV collected by the CMS experiment at the LHC, corresponding to an
integrated luminosity of 5.3 inverse femtobarns. The known Xi(b)^- baryon is
reconstructed via the decay chain Xi(b)^- to J/psi Xi^- to mu^+ mu^- Lambda^0 pi^-,
with Lambda^0 to p pi^-. A peak is observed in the distribution of the difference
between the mass of the Xi(b)^- pi^+ system and the sum of the masses of the Xi(b)^-
and pi^+, 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 J^P=3/2^+ companion of the Xi(b).