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Measurement of the b baryon lifetime and branching fractions in Z decays


Using approximately 4 million hadronic Z decays recorded with the aleph detector from 1991 through 1995, the lifetime of the b baryon is measured with three independent methods. From the impact parameter distribution of candidate leptons in 1063 events with \(\Lambda\ell^-\) combinations, the average b baryon lifetime is measured to be \(1.20\pm{0.08}\pm{0.06}\) ps. From a sample of 193 fully reconstructed \(\Lambda^+_{\rm c}\) candidates correlated with a lepton and a sample of 46 \(\Lambda\ell^+\ell^-\) combinations, the \(\Lambda_{\rm b}\) lifetime is measured to be \(1.21\pm{0.11}\) ps. The product branching fractions to these final states are \({\rm Br(b\to \Lambda_{\rm b}}\cdot{\rm BR (\Lambda_{\rm b} \to \Lambda\ell^-\overline\nu X}) = 0.326\pm{0.016}\pm{0.039}\)% for the first sample and \({\rm Br(b\to \Lambda_{\rm b}}\cdot{\rm BR(\Lambda_{ \rm b} \to \Lambda^+_{\rm c}\ell^-\overline\nu X}) =0.86\pm{0.07}\pm{0.14}\)% for the second and third samples combined.

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Received: 15 August 1997 / Online publication: March 10, 1998

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The ALEPH Collaboration., Barate et al., R. Measurement of the b baryon lifetime and branching fractions in Z decays. Eur. Phys. J. C 2, 197–211 (1998).

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  • Impact Parameter
  • Parameter Distribution
  • Independent Method
  • Candidate Lepton
  • Impact Parameter Distribution