QCD anatomy of $B\to X_s\gamma$ decays

Abstract

We present an updated next-to-leading order analysis of the B -> X_s gamma\nbranching ratio and photon spectrum, including consistently the effects of\nFermi motion in the heavy-quark expansion. For the Standard Model, we obtain\nB(B -> X_s gamma) = (2.57+-0.26^{+0.31}_{-0.36}) * 10^{-4} for the integral\nover the high-energy part of the photon spectrum with E_gamma^{lab} > 2.2 GeV,\nwhere the first error reflects the uncertainty in the input parameters, and the\nsecond one the uncertainty in the calculation of Fermi motion. This prediction\nagrees with the CLEO measurement of the same quantity within one standard\ndeviation. From a reanalysis of the CLEO data, we obtain for the total\nbranching ratio B(B -> X_s gamma) = (2.62+-0.60_{exp}^{+0.37}^{-0.30{th}}) *\n10^{-4} using the measured rate above 2.2 GeV, and\n(2.66+-0.56_{exp}^{+0.43}_{-0.48{th}}) * 10^{-4} using a fit to the photon\nenergy spectrum. Both values are consistent with the Standard Model prediction\nof (3.29+-0.33) * 10^{-4}. Our analysis contains an improved discussion of\nrenormalization scale dependence and QED corrections. We also discuss the\nsensitivity of the branching ratio and photon spectrum to hadronic parameters\nsuch as the b-quark mass, and to possible contributions from New Physics beyond\nthe Standard Model.\n