Improved measurement of the $B^0$ and $B^+$ meson lifetimes

The lifetimes of the B-0 and B+ mesons have been measured with the ALEPH detector at LEP, using approximately 3 million hadronic Z decays collected in the period 1991-1994. In the first of three methods, semileptonic decays of B-0 and B+ mesons were partially reconstructed by identifying events containing a lepton with an associated D*(-) or (D) over bar(0) meson. The second method used fully reconstructed B-0 and B+ mesons. The third method, used to measure the B-0 lifetime, employed a partial reconstruction technique to identify B-0 --> D*(-)pi(+)X decays. The combined results are tau(0) = 1.55 +/- 0.06 +/- 0.03 ps, tau(+) = 1.58 +/- 0.09 +/- 0.03 ps, tau(+)/tau(0) = 1.03 +/- 0.08 +/- 0.02