Time-dependent CP asymmetry in B→K*γ as a (quasi)null test of the Standard Model

We calculate the dominant Standard Model contributions to the time-dependent CP asymmetry in B-0 -> K-*0 gamma, which is O(1/m(b)) in QCD factorisation. We find that, including all relevant hadronic effects, in particular from soft gluons, the asymmetry S is very small, S = -0.022 +/- 0.012 0.01(-0.01)(+0), and smaller than suggested recently from dimensional arguments in a 1/m(b) expansion. Our result implies that any significant deviation of the asymmetry from zero, and in particular a confirmation of the current experimental central value, S-HFAG = -0.28 +/- 0.26, would constitute a clean signal for new physics. (c) 2006 Elsevier B.V. All rights reserved.