Measurement of the (B)over-bar(0) and B- meson lifetimes

The lifetimes of the (B) over bar (0) and B- mesons are measured using a sample of about four million hadronic Z decays collected from 1991 to 1995 with the ALEPH detector at LEP. The data sample has been recently reprocessed, achieving a substantial improvement in the tracking performance. Semileptonic decays of (B) over bar (0) and B- mesons are partially reconstructed by identifying events containing a lepton with an associated D*(+) or D-0 meson, The proper time of the B meson is estimated from the measured decay length and the momentum of the D-lepton system. A fit to the proper time of 1880 D*(+)l(-) and 2856 D(0)l(-) candidates yields the following results: tau ((B) over bar0) = 1.518 +/- 0.053 +/- 0.034 ps, tau (B-) = 1.648 +/- 0.049 +/- 0.035 ps, tau (B-)/tau ((B) over bar0) = 1.085 +/- 0.059 +/- 0.018. (C) 2000 Elsevier Science B.V. All rights reserved.