Improved measurement of the $\bar{B}^0$ and $B^{-}$ meson lifetimes

The lifetimes of theB 0 andB + mesons have been measured with theAleph detector at LEP, using approximately 3 million hadronic Z decays collected in the period 1991–1994. In the first of three methods, semileptonic decays ofB 0 andB + mesons were partially reconstructed by identifying events containing a lepton with an associatedD*− orD¯0 meson. The second method used fully reconstructedB 0 andB + mesons. The third method, used to measure theB 0 lifetime, employed a partial reconstruction technique to identifyB 0→D*− π + X decays. The combined results are τ0=1.55±0.06±0.03ps,τ+=1.58±0.09±0.03ps,τ+τ0=1.03±0.08±0.02.