On the impact of power corrections in the prediction of B->K*mu+mu- observables

TL;DR

This paper systematically assesses power corrections in B->K*mu+mu- decay predictions, demonstrating that their impact is manageable and discussing how to distinguish between hadronic effects and potential new physics in recent anomalies.

Contribution

It introduces a method to include factorisable power corrections in QCD factorisation and analyzes their influence on angular observables, clarifying uncertainties and scheme dependence.

Findings

Power corrections can be controlled with proper schemes.

Uncertainties from power corrections are smaller than previously thought.

Strategies are proposed to differentiate charm-resonance effects from New Physics.

Abstract

The recent LHCb angular analysis of the exclusive decay B->K^*mu+mu- has indicated significant deviations from the Standard Model expectations. Accurate predictions can be achieved at large K*-meson recoil for an optimised set of observables designed to have no sensitivity to hadronic input in the heavy-quark limit at leading order in alpha_s. However, hadronic uncertainties reappear through non-perturbative Lambda_QCD/m_b power corrections, which must be assessed precisely. In the framework of QCD factorisation we present a systematic method to include factorisable power corrections and point out that their impact on angular observables depends on the scheme chosen to define the soft form factors. Associated uncertainties are found to be under control, contrary to earlier claims in the literature. We also discuss the impact of possible non-factorisable power corrections, including an estimate of charm-loop effects. We provide results for angular observables at large recoil for two different sets of inputs for the form factors, spelling out the different sources of theoretical uncertainties. Finally, we comment on a recent proposal to explain the anomaly in B->K*mu+mu- observables through charm-resonance effects, and we propose strategies to test this proposal identifying observables and kinematic regions where either the charm-loop model can be disentangled from New Physics effects or the two options leave different imprints.