Measurement of V_{cb} from the decay process \bar{B^0} -> D^{*+} \ell^- \bar{\nu}

TL;DR

This paper reports a precise measurement of the CKM matrix element |V_{cb}| and the branching ratio for the decay ^0 ^{*+} ll^- ar{ u} using data from the DELPHI detector, including analysis of differential cross-sections and form factors.

Contribution

The study provides the first detailed measurement of ^0 ^{*+} ll^- ar{ u} decay parameters with unfolded differential distributions and improved precision.

Findings

|V_{cb}| = (39.0 .0) .6 .3 imes 10^{-3}

Branching ratio BR(^0 ^{*+} ll^- ar{ u}) = (4.70 .13 .36) %

Differential cross-section and form factor dependences obtained

Abstract

A new precise measurement of |V_{cb}| and of the branching ratio BR(\bar{B^0} -> D^{*+} \ell^- \bar{\nu_\ell}) has been performed using a sample of about 5000 semileptonic decays \bar{B^0} -> D^{*+} \ell^- \bar{\nu_\ell}, selected by the DELPHI detector at LEP I by tagging the soft pion from D^{*+} -> D^0 \pi^+. The results are: V_{cb}=(39.0 +/- 1.5 (stat.) ^{+2.5}_{-2.6} (syst. exp.) +/- 1.3 (syst. th.)) x 10^{-3} BR(\bar{B^0} -> D^{*+} \ell^- \bar{\nu_\ell})=(4.70 +/- 0.13 (stat.) ^{+0.36}_{-0.31} (syst. exp.))% The analytic dependences of the differential cross-section and of the Isgur Wise form factor as functions of the variable w = v_{B^0}.v_{D^*} have also been obtained by unfolding the experimental resolution.