Measurement of the $\overline B^{0}$ and $B^-$ Meson Lifetimes

The lifetimes of the \b0 \ and \bp\ mesons have been measured with the \aleph\ detector at LEP, using three different methods. In the first method, semileptonic decays of \b0 \ and \bp\ mesons were partially reconstructed by identifying events containing a lepton with an associated \ds\ or \d0 \ meson. The proper time of the B meson was estimated from the measured decay length and the B meson momentum, reconstructed using an energy flow technique. The second method uses fully reconstructed \bz\ and \bp\ mesons. The third method, used to measure the \bz\ lifetime, uses a partial reconstruction technique to identify $\bz\to D^{*+}\pi^- X$ decays. The combined preliminary results are: \begin{eqnarray*} \t0 & = & 1.54\pm 0.07 \mathrm{\ ps} \\ \tp & = & 1.58\pm 0.09 \mathrm{\ ps} \\ \trat & = & 1.03\pm 0.08 \end{eqnarray*} %