The decay overline B to overline K {ell^{ + }}{ell^{ - }} at low hadronic recoil and model-independent ∆B = 1 constraints

摘要

We study the decay ( overline B to overline K {ell^{ + }}{ell^{ - }} ) for ℓ = e, μ, τ with a softly recoiling kaon, that is, for high dilepton invariant masses ( sqrt {{{q^{{2}}}}} ) of the order of the b-quark mass. This kinematic region can be treated within an operator product expansion and simplified using heavy quark symmetry, leading to systematic predictions for heavy-to-light processes such as ( overline B to {overline K^{{left( * right)}}}{ell^{ + }}{ell^{ - }} ). We show that the decay rates of both ( overline B to {overline K^{ * }}{ell^{ + }}{ell^{ - }} ) and ( overline B to overline K {ell^{ + }}{ell^{ - }} ) decays into light leptons depend on a common combination of short-distance coefficients. The corresponding CP-asymmetries are hence identical. Furthermore we present low recoil predictions for ( overline B to overline K {ell^{ + }}{ell^{ - }} ) observables, including the flat term in the angular distribution which becomes sizable for taus. We work out model-independently the constraints on ΔB = 1 operators using the most recent data from the experiments BaBar, Belle, CDF and LHCb. For constructive interference with the standard model, generic new physics is pushed up to scales above 44 TeV at 95% CL. Assuming none or small CP-violation we obtain a lower bound on the position of the zero of the forward-backward asymmetry of ( {overline B^0} to {overline K^{{ * 0}}}{ell^{ + }}{ell^{ - }} ) decays as ( q_0^2 > {1}.{7} ) GeV2, which improves to ( q_0^2 > 2.6 ) GeV2 for a standard model-like sign b → sγ amplitude.