B-meson lifetime from the MAC detector

The MAC detector has been run at PEP at √s = 29 GeV enough to collect 108 pb-1 integrated luminosity of e+e- collisions, and a sample of about 50,000 multihadron events was isolated. By the flavor-tagging procedure direct leptons associated with these events were identified: muons by their lack of interaction in the iron of the hadron calorimeter and appearance as clear tracks in a system of drift tubes surrounding the calorimeter. Electrons are identified in a lead-proportional shower chamber immediately surrounding the central drift chamber (of 1 m diameter and with first layer approx. 12 cm from the beam. The b-enriched sample is selected from these as having a lepton over 2 GeV/c with momentum transverse to the event thrust axis over 1.5 GeV/c. This procedure gives 155 muon and 113 electron events, estimated by Monte Carlo technique to be respectively 72% and 63% pure b-quark associated. The impact parameter delta of the lepton track with respect to the average beam position, as determined from Bhabha scattering events from the same exposure, was then plotted. Allowing for contributions from c-quark and background events, the combined data gives T/sub b/ = (1.8 +- 0.6 +- 0.4) x 10-12sec where the last error is the estimated systematic error