Improved 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, using approximately 3 million hadronic Z decays collected in the period 1991-1994. In the first of three methods, semileptonic decays of B0 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 B0 and B+ mesons. The third method, used to measure the B0 lifetime, employed a partial reconstruction technique to identify B0 --> D*(-)pi(+)X decays. The combined results are tau(B0) = 1.55 +/- 0.06 +/- 0.03 ps, tau(B+) = 1.58 +/- 0.09 +/- 0.03 ps, tau(B+)/tau(B0) = 1.03 +/- 0.08 +/- 0.02.