A measurement of B⁺ and B⁰ lifetimes using$\bar D\ell ^ +$ events

Abstract

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$\bar D^{^0 } \ell ^ +$ and D^*ℓ⁺ events originate mainly from the semileptonic decays of B⁺ and B⁰ mesons, respectively. From the reconstructed B decay length and the estimated B momentum, taking into account the dilution due to B decays into$\bar D^{^{**} } \ell ^ + v$, the following B meson lifetimes and lifetime ratio are measured:

$$\begin{gathered} \tau (B^ + ) = 1.61_{ - 0.16}^{ + 0.16} (stat.) \pm 0.12(syst.) ps \hfill \\ \tau (B^0 ) = 1.61_{ - 0.13}^{ + 0.14} (stat.) \pm 0.08(syst.) ps \hfill \\ \tau (B^ + )/\tau (B^0 ) = 1.00_{ - 0.15}^{ + 0.17} (stat.) \pm 0.10(syst.) \hfill \\ \end{gathered} $$

and an average lifetime of B⁺ and B⁰ mesons is obtained:

$$\tau (B) = 1.61_{ - 0.07}^{ + 0.08} (stat.) \pm 0.05(syst.) ps$$