P. Abreu et al., PRODUCTION OF STRANGE B-BARYONS DECAYING INTO XI- +-L-/+ PAIRS AT LEP/, Zeitschrift fur Physik. C, Particles and fields, 68(4), 1995, pp. 541-553
An excess of events containing, in a jet, a same-sign Xi(-/+) - l(-/+)
pair as compared to those with an opposite-sign Xi(-/+) - l(-/+) pair
has been observed in an analysis of 1.7 million hadronic Z(o) decays
collected by the DELPHI detector at LEP between 1991 and 1993 inclusiv
e. The probability for this signal to come from non B-baryon decays is
less than 5 x 10(-4). The measured production fraction corresponds to
: P(b --> B - baryon) x BR(B - baryon --> Xi(-) l(-) X) = (5.9 +/- 2.1
+/- 1.0) x 10(-4), per lepton species, averaged for electrons and muo
ns and assuming the two channels have an equal contribution. Semilepto
nic decays of Lambda(b) baryons can account for less than 10% of these
events and the major part of the signal has to originate from Xi(b) s
emileptonic decays, Using the subsample of these events where the Xi(-
/+) trajectory has been measured in the Vertex Detector, the lifetime
of B-baryons producing a Xi(-/+) in their semileptonic decay final sta
te is found to be: tau(B - baryon --> Xi(-) l(-) X) = 1.5(-0.4)(+0.7)
+/- 0.3 ps.