A measurement of B+^{+} and B0^{0} lifetimes using D‾\overline{D}l+^{+} events

A measurement of B meson lifetimes is presented using data collected from 1991 to 1993 by the DELPHI detector at the LEP collider. Samples of events with a D meson and a lepton in the same jet are selected where \overline{\mathrm{D}}^0 \ell^+ and \mathrm{D}^{*-} \ell^+ events originate mainly from the semileptonic decays of B^+ and B^0 mesons, respectively. From the reconstructed B decay length and the estimated B momentum, taking into account the dilution due to B decays into \overline{\mathrm{D}}^{**} \ell^+ \nu, the following B meson lifetimes and lifetime ratio are measured: \begin{eqnarray*} \tau(\mathrm{B}^+) &=& 1.61^{+0.16}_{-0.16} \;(\mathrm{stat}.) \pm 0.12 \;(\mathrm{syst.}) \;\mathrm{ ps} \\ \tau(\mathrm{B}^0) &=& 1.61^{+0.14}_{-0.13} \;(\mathrm{stat}.) \pm 0.08 \;(\mathrm{syst.}) \;\mathrm{ ps} \\ \tau(\mathrm{B}^+) / \tau(\mathrm{B}^0) &=& 1.00^{+0.17}_{-0.15} \;(\mathrm{stat.}) \pm 0.10 \;(\mathrm{syst.}) \end{eqnarray*} and an average lifetime of B^+ and B^0 mesons is obtained: \begin{eqnarray*} \tau(\mathrm{B}) = 1.61^{+0.08}_{-0.07} \;\mathrm{(stat.)} \pm 0.05 \;\mathrm{(syst.) \;ps} \end{eqnarray*