QCD uncertainties in the prediction of B --> K^* mu^+ mu^- observables

TL;DR

This paper addresses the impact of QCD uncertainties, particularly from form factors and charm loops, on the precision of B --> K^* mu^+ mu^- decay predictions, crucial for interpreting deviations from the Standard Model.

Contribution

It introduces a systematic method to include factorisable power corrections to form factors within QCD factorisation, analyzing scheme dependence and charm-loop effects.

Findings

Power corrections significantly affect observable predictions.

Scheme choice influences the size of uncertainties.

Charm-loop effects are non-negligible in precise calculations.

Abstract

The recent LHCb angular analysis of the exclusive decay B --> K^* mu^+ mu^- has indicated significant deviations from the Standard Model expectations. In order to give precise theory predictions, it is crucial that uncertainties from non-perturbative QCD are under control and properly included. The dominant QCD uncertainties originate from the hadronic B --> K^* form factors and from charm loops. We present a systematic method to include factorisable power corrections to the form factors in the framework of QCD factorisation and study the impact of the scheme chosen to define the soft form factors. We also discuss charm-loop effects.