New-physics contributions to the forward-backward asymmetry in B → K*μ⁺μ⁻

Abstract

We study the forward-backward asymmetry (A_FB) and the differential branching ratio (DBR) in B → K*μ⁺μ⁻ in the presence of new physics (NP) with different Lorentz structures. We consider NP contributions from vector-axial vector (VA), scalarpseudoscalar (SP), and tensor (T) operators, as well as their combinations. We calculate the effects of these new Lorentz structures in the low-q² and high-q² regions, and explain their features through analytic approximations. We find two mechanisms that can give a significant deviation from the standard-model predictions, in the direction indicated by the recent measurement of AFB by the Belle experiment. They involve the addition of the following NP operators: (i) VA, or (ii) a combination of SP and T (slightly better than T alone). These two mechanisms can be distinguished through measurements of DBR in B → K*μ⁺μ⁻ and A_FB in B → K*μ⁺μ⁻.