A measurement ofB meson production and lifetime usingDl ⁻ events inZ ⁰ decays

Abstract

A study ofB meson decays intoDl X final states is presented. In these events, neutral and chargedD mesons originate predominantly fromB ⁺ andB ⁰ decays, respectively. The dilution of this correlation due toD ^** production has been taken into account. From 263 700 hadronicZ ⁰ decays collected in 1991 with the DELPHI detector at the LEP collider, 92D ⁰→K ^-π⁺, 35D ⁺→K ^-π⁺π⁺ and 61D ^*0→D ⁰π⁺ followed byD ⁰→K ^-π⁺ orD ⁰→K ^-π⁺π⁺π^-, are found with an associated lepton of the same charge as the kaon. From theD ⁰ l ^- andD ^*+ l ^-, the probabilityf _d that ab quark hadronizes into aB ⁻ (or$\bar B^0$) meson is found to be 0.44 ±0.08±0.09, corresponding to a total (B _s+Λ _b ) hadronization fraction of 0.12 ^+0.24_−0.12 . By reconstructing the energy of eachB meson, theb quark fragmentation is directly measured for the first time. The mean value of theB meson energy fraction is:

$$\left\langle {X_E (B)} \right\rangle = 0.695 \pm 0.015(stat.) \pm 0.029(syst.)$$

ReconstructingD-lepton vertices, the followingB lifetimes are measured:

$$\begin{gathered} \tau (B) = 1.27_{ - 0.18}^{ + 0.22} (stat.) \pm 0.15(syst.)ps, \hfill \\ where\bar B \to D^0 \ell ^ - X, \hfill \\ \tau (B) = 1.18_{ - 0.27}^{ + 0.39} (stat.) \pm 0.15(syst.)ps, \hfill \\ where\bar B \to D^ + \ell ^ - X, \hfill \\ \tau (B) = 1.19_{ - 0.19}^{ + 0.25} (stat.) \pm 0.15(syst.)ps \hfill \\ where\bar B \to D^{* + } \ell ^ - X, \hfill \\ \end{gathered} $$

and an average τ(B)=1.23 ^+0.14_−0.13 (stat.)±0.15(syst.) ps is found. Allowing for decays into$D**\ell ^ - \bar v$, theB ⁺ andB ⁰ lifetimes are:

$$\begin{gathered} \tau (B^ + ) = 1.30_{ - 0.29}^{ + 0.33} (stat.) \pm 0.15(syst.\exp .) \hfill \\ \pm 0.05(syst.D**)ps, \hfill \\ \tau (B^0 ) = 1.17_{ - 0.23}^{ + 0.29} (stat.) \pm 0.51(syst.\exp .) \hfill \\ \pm 0.05(syst.D**)ps, \hfill \\ \tau (B^ + )/\tau (B^0 ) = 1.11_{ - 0.39}^{ + 0.51} (stat.) \pm 0.05(syst.\exp .) \hfill \\ \pm 0.10(syst.D**)ps. \hfill \\ \end{gathered} $$