Effect of supersymmetric phases on the direct CP asymmetry of B → Xγ

We investigate the effect of supersymmetric CP violating phases on the inclusive decay B --> X(d)gamma. Although such a decay contains a large background from B --> X(s)gamma, if isolated it may exhibit sizeable CP violation, both in the Standard Model (SM) and in the context of models beyond the SM. With unconstrained supersymmetric CP violating phases we show that the direct CP asymmetry (A(CP)) lies in the region -40% less than or equal to A(CP) less than or equal to 40%, where a positive asymmetry would constitute a clear signal of physics beyond the SM. Even if a direct measurement of B --> X(d)gamma proves too difficult experimentally, its asymmetry contributes non-negligibly to the measurements of A(CP) for B --> X(s)gamma, and thus should be included in future analyses. We show that there may be both constructive and destructive interference between A(CP)(d gamma) and A(CP)(s gamma). (C) 2001 Published by Elsevier Science B.V.