Measurement of the B0 and B− meson lifetimes

The lifetimes of the B0 and B- mesons have been measured with the ALEPH detector at LEP. Semileptonic decays of B0 and B- mesons were partially reconstructed by identifying events containing a lepton with an associated D*+ or D0 meson. The proper time of the B meson was estimated from the measured decay length and the momentum and mass of the D-lepton system. A fit to the proper time of 77 D*+l- and 77 D0l- candidates, combined with a constraint on the lifetime ratio (τ-/τ0) arising from the relative rates of observed D*+l- and D0l- events, yielded the following lifetimes: τ0=1.52-0.18+0.20(stat.)-0.13+0.07(syst.) ps, τ- = 1.47-0.19+0.22(stat.)-0.14+0.15(syst.) ps, τ-/τ0 = 0.96-0.15+0.19(stat.)-0.12+0.18(syst.).