New-physics contributions to the forward-backward asymmetry in B -> K* mu+ mu-

TL;DR

This paper investigates how various new physics operators could explain deviations in the forward-backward asymmetry in B -> K* mu+ mu- decays, offering potential explanations for recent experimental results.

Contribution

It analyzes the effects of vector, scalar, and tensor new physics operators on AFB and DBR in B decays, identifying mechanisms that could account for observed deviations.

Findings

VA operators can significantly alter AFB.

Combination of SP and T operators can also produce notable effects.

Two main mechanisms identified that could explain experimental deviations.

Abstract

We study the forward-backward asymmetry (AFB) and the differential branching ratio (DBR) in B -> K* mu+ mu- in the presence of new physics (NP) with different Lorentz structures. We consider NP contributions from vector-axial vector (VA), scalar-pseudoscalar (SP), and tensor (T) operators, as well as their combinations. We calculate the effects of these new Lorentz structures in the low-q^2 and high-q^2 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* mu+ mu- and AFB in B -> K mu+ mu-.