Direct CP Asymmetry of B -> X_d,s \gamma in a model with Vector quarks

Abstract

We investigate the effect of vector quarks on the inclusive decays B -> X_d,s \gamma. We show that the branching ratio of B -> X_d \gamma can differ sizably from the SM and MSSM predictions, being enhanced to present experimental observability or suppressed such that present runs of the B factories would not observe it. Current measurements of the direct CP asymmetry (A_CP) for B -> X_s \gamma are sensitive to the contribution from B -> X_d \gamma. For a sufficiently enhanced BR(B -> X_d \gamma) we show that the dominant contribution to the combined asymmetry may be from B -> X_d \gamma. Thus any large value for A_CP should not immediately be attributed to B -> X_s \gamma, which stresses the importance of good K/pi separation.