Determination of the Branching Fraction for Inclusive Decays B X_s} gamma.pdf

BABAR-CONF-02/026 SLAC-PUB-9301 July 2002 2 0 0 2 l u Determination of the Branching Fraction for Inclusive Decays J B → X γ 5 s 2 1 v The BABAR Collaboration 6 7 0 July 24 2002 7 0 2 0 / x Abstract e - p We present a preliminary determination of the inclusive branching fraction for the rare radiative e penguin transition B → X γ . The measurement is based on a data sample of 60 million BB h s : pairs collected between 1999 and 2001 with the BABAR detector at the PEP-II asymmetric-energy v e+e− B Factory at SLAC. We study events containing a high-energy photon from one B (or i X B) decay and a tagging primary lepton from the decay of the other B meson. By this means, r we are able to reduce a significant component of the background without introduction of model a dependent uncertainties in the event selection efficiency. We determine the branching fraction B (B → X γ )=[3.88 ± 0.36(stat.) ± 0.37(syst.) ±0.43 (model)] × 10−4 , which is consistent with s 0.23 Standard Model predictions and provides a constraint on possible new physics contributions to the electromagnetic penguin amplitude in B decays. Contributed to the 31st International Conference on High Energy Physics,