A Comparative Study of the Decays Β→(K,K^*)l^+ l^- in Standard Model and Supersymmetric Theories

Using improved theoretical calculations of the decay form factors in the Lightcone-QCD sum rule approach, we investigate the decay rates, dilepton invariant mass spectra and the forward-backward (FB) asymmetry in the decays Β→(K,K^*)l^+ l^- (l^±=e^±,μ^±,τ^±) in the standard model (SM) and a number of popular variants of the supersymmetric (SUSY) models.Theoretical precision on the differential decay rates and FB-asymmetry are worked out in these theories taking into account various parameteric uncertainties. We argue that the FB-asymmetry in Β→K^* l^+ l^- provides a precision test of the SM and its measurement may reveal new physics.In particular, the presently allowed large-tan β solutions in SUGRA models yield FB-asymmetries which are characteristically different from the corresponding ones in SM. We also emphasize the role of exclusive rare decays, in particular, the present experimental bounds on the branching ratio B(Β→K^* μ^+ μ^-) in constraining the parameters of the SUSY models.