Looking for Novel CP-Violating Effects in B->K^*l^+l^-

Abstract

The CP-violating asymmetries in the exclusive decay B->K^*l^+l^- (l=e,mu,tau) are predicted to be exceedingly small in the standard model (SM), thereby offering an opportunity to assess various new-physics scenarios. We derive quantitative predictions for various integrated observables in B->K^*mu^+mu^- decay in the presence of physics beyond the SM with additional CP phases and an extended operator basis. In particular, a model-independent analysis of CP asymmetries that require the presence of unitarity phases, in addition to CP violation, is performed. We find that in the low dimuon invariant mass region 2m_mu<M_{mu^+mu^-}<M_{J/psi}, the CP asymmetries are highly suppressed by small dynamical phases, assuming that new physics is unlikely to significantly alter the Wilson coefficients of the operators governing two-body hadronic B decays. Taking into account current experimental data on the measured b->s gamma rate and the upper limit on BR(B^0->K^{*0}mu^+mu^-), CP-violating effects of a few per cent are estimated, even in the presence of new physics with CP phases of O(1). By contrast, in the high dimuon invariant mass region M_{psi'}<M_{mu^+mu^-}<(M_B-M_{K^*}) significant CP-violating effects are possible. Given a branching ratio of 1.8 x 10^{-6}, the CP asymmetries can be quite substantial (\sim 20% or more), and thus may serve as a means of discovering physics transcending the SM.