Measurement of the direct CP asymmetry in B ¯ →xs+dγ decays with a lepton tag

Abstract

We report the measurement of the direct CP asymmetry in the radiative B¯→Xs+dγ decay using a data sample of (772±11)×106 BB¯ pairs collected at the (4S) resonance with the Belle detector at the KEKB asymmetric-energy e+e- collider. The CP asymmetry is measured as a function of the photon energy threshold. For Eγ∗≥2.1GeV, where Eγ∗ is the photon energy in the center-of-mass frame, we obtain ACP(B¯→Xs+dγ)=(2.2±3.9±0.9)%, consistent with the standard model prediction.