Production of Xi_c^0 and Xi_b in Z decays and lifetime measurement of Xi_b

The charmed strange baryon Ξ 0 c was searched for in the decay channel Ξ 0 c → Ξ −π +, and the beauty strange baryon Ξb in the inclusive channel Ξb → Ξ −` −ν¯X, using the 3.5 million hadronic Z events collected by the DELPHI experiment in the years 1992–1995. The Ξ − was reconstructed through the decay Ξ − → Λπ −, using a constrained fit method for cascade decays. An iterative discriminant analysis was used for the Ξ 0 c and Ξb selection. The production rates were measured to be fΞ0 c ×BR(Ξ 0 c → Ξ −π +) = (4.7±1.4(stat.)±1.1(syst.))×10−4 per hadronic Z decay, and BR(b → Ξb)×BR(Ξb → Ξ −` −X) = (3.0±1.0(stat.)±0.3(syst.))×10−4 for each lepton species (electron or muon). The lifetime of the Ξb baryon was measured to be τΞb = 1.45+0.55 −0.43(stat.)± 0.13(syst.) ps. A combination with the previous DELPHI lifetime measurement gives τΞb = 1.48+0.40 −0.31(stat.)±0.12(syst.) ps.