Direct observation of the strange b baryon Xi(-)(b)

• Published in: Physical review letters Vol. 99; no. 5; p. 052001
• Main Authors: Abazov, V. M., Åsman, Barbro, Bélanger-Champagne, Camille, Clément, Christophe, Gollub, Nils, Hansson, Per, Strandberg, Jonas, Strandberg, Sara, Zverev, E. G., et al
• Format: Journal Article
• Language: English
• Published: 2007
• Subjects: Elementarpartikelfysik; Elementary particle physics; Fysik; LIFETIME; NATURAL SCIENCES; NATURVETENSKAP; PHYSICS; Z-DECAYS
• ISSN: 0031-9007; 1079-7114
• DOI: 10.1103/PhysRevLett.99.052001

We report the first direct observation of the strange b baryon Xi(-)(b)(Xi) over bar (+)(b)). We reconstruct the decay Xi(-)(b)-->J/psi Xi(-), with J/psi-->mu(+)mu(-), and Xi(-)-->Lambda pi(-)-->p pi(-)pi(-) in p (p) over bar collisions at root 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) Xi(-)(b) candidates at a mass of 5.774 +/- 0.011(stat) +/- 0.015(syst) GeV. The significance of the observed signal is 5.5 sigma, equivalent to a probability of 3.3 x 10(-8) of it arising from a background fluctuation. Normalizing to the decay Lambda(b)-->J/psi Lambda, we measure the relative rate sigma(Xi(-)(b))xB(Xi(-)(b)-->J/psi Xi)/ sigma(Lambda(b))xB(Lambda(b)-->J/psi Lambda) = 0.28 +/- 0.09(stat)(-0.08)(+0.09)(syst).