Direct Observation of the Strange b Baryon Ξ_b^-

Authors

V. M. Abazov, Joint Institute for Nuclear Research, Dubna, Russia
Kenneth A. Bloom, University of Nebraska-LincolnFollow
Gregory R. Snow, University of Nebraska-LincolnFollow
D0 Collaboration

Date of this Version

8-3-2007

Comments

Published in PHYSICAL REVIEW LETTERS 99, 052001 (2007). © 2007 The American Physical Society. Used by permission.

Abstract

We report the first direct observation of the strange b baryon Ξ_b^-( Ξ_b⁺). We reconstruct the decay Ξ_b^- → J/ψΞ^-, withJ/ψ → μ⁺ μ^-, and Ξ^- → Λ π ^- → p π^-+ π^+- in pp̅ collisions at √s = 1.96 TeV. Using 1.3 fb^-1 of data collected by the D0 detector, we observe 15.2 ± 4.4(stat) _-0.4^+1.9(syst) Ξ_b^- candidates at a mass of 5.774 ± 0.:011(stat) ± 0.015(syst) GeV. The significance of the observed signal is 5.5 σ, equivalent to a probability of 3.3 x 10^-8 of it arising from a background fluctuation. Normalizing to the decay Λ_b → J/ψΛ, we measure the relative rate [σ(Ξ_b^-)x ℬ(Ξ_b^- → J/ψΞ^-)]/[σ (Λ_b) x ℬ(Λ_b→ J/ψ Λ)] = 0.28 ± 0.09 (stat) _-0.08^+0.09 (syst).