Measurement of the inclusive semileptonic branching fraction of B mesons using fully reconstructed B-mesons as tags in the BABAR experiment

The BABAR experiment at SLAC provides an opportunity for measurement of the Standard Model parameters describing CP violation. A method of measuring the CKM matrix element |V _cb| using Inclusive Semileptonic B decays in events tagged by a fully reconstructed decay of one of the B mesons is presented here. This mode is considered to be one of the most powerful approaches due to its large branching fraction, simplicity of the theoretical description and very clean experimental signatures. Using fully reconstructed B mesons to flag BB¯ event we were able to produce the spectrum and branching fraction for electron momenta P_C.M.S. > 0.5 GeV/c. Extrapolation to the lower momenta has been carried out with Heavy Quark Effective Theory. The branching fractions are measured separately for charged and neutral B mesons. For 82 fb−1 of data collected at BABAR we obtain: BR (B± → Xe$n$) = 10.63 ± 0.24 ± 0.29%, BR( B0 → Xe$n$) = 10.68 ± 0.34 ± 0.31%, averaged BR( B → Xe$n$) = 10.65 ± 0.19 ± 0.27%, ratio of Branching fractions BR(B±)/BR( B0) = 0.996 ± 0.039 ± 0.015 (errors are statistical and systematic, respectively). We also obtain V _cb = 0.0409 ± 0.00074 ± 0.0010 ± 0.000858 (errors are: statistical, systematic and theoretical).