, Volume 44, Issue 3, pp 299-309

Production of \(\Xi{_c^0}\) and \(\Xi{_b}\) in Z decays and lifetime measurement of \(\Xi{_b}\)

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The charmed strange baryon \(\Xi{_c^0}\) was searched for in the decay channel \(\Xi{_c^0} \rightarrow \Xi^- \pi^ + \) , and the beauty strange baryon \(\Xi{_b}\) in the inclusive channel \(\Xi_b \rightarrow \Xi^{-} \ell^{-} \bar{\nu} X\) , using the 3.5 million hadronic Z events collected by the DELPHI experiment in the years 1992-1995. The \(\Xi^-\) was reconstructed through the decay \(\Xi^- \rightarrow \Lambda \pi^-\) , using a constrained fit method for cascade decays. An iterative discriminant analysis was used for the \(\Xi{_c^0}\) and \(\Xi{_b}\) selection. The production rates were measured to be \(f_{\Xi{_c^0}} \times\) BR \((\Xi{_c^0} \rightarrow \Xi^- \pi^ + ) = (4.7 \pm 1.4 ({\rm stat.}) \pm 1.1 ({\rm syst.}))\times 10^{-4}\) per hadronic Z decay, and BR \((b \rightarrow \Xi{_b}) \times\) BR \((\Xi{_b} \rightarrow \Xi^- \ell^- X) = (3.0 \pm 1.0({\rm stat.}) \pm 0.3({\rm syst.}))\times 10^{-4}\) for each lepton species (electron or muon). The lifetime of the \(\Xi{_b}\) baryon was measured to be \( \tau_{\Xi{_b}} = 1.45{^{ + 0.55}_{-0.43}} ({\rm stat.}) \pm 0.13 ({\rm syst.})\) ps. A combination with the previous DELPHI lifetime measurement gives \( \tau_{\Xi{_b}} = 1.48{^{ + 0.40}_{-0.31}} ({\rm stat.}) \pm 0.12 ({\rm syst.})\) ps.

Received: 11 January 2005, Revised: 1 June 2005, Published online: 6 October 2005