$B\to K^* \ell^+ \ell^-$ decays at large recoil in the Standard Model: a theoretical reappraisal

TL;DR

This paper reevaluates the theoretical uncertainties in Standard Model predictions for $B o K^* \, \ell^+ \ell^-$ decays at low recoil, emphasizing the impact of hadronic effects and power corrections on observables.

Contribution

It provides a detailed numerical analysis of uncertainties and demonstrates that non-factorizable power corrections can account for current experimental data within the Standard Model.

Findings

Optimized observables are significantly affected by hadronic uncertainties.

Power corrections of expected magnitude can explain experimental results.

The $q^2$ dependence of corrections may mimic shifts in Wilson coefficients.

Abstract

We critically reassess the theoretical uncertainties in the Standard Model calculation of the $B \to K^* \ell^+ \ell^-$ observables, focusing on the low $q^2$ region. We point out that even optimized observables are affected by sizable uncertainties, since hadronic contributions generated by current-current operators with charm are difficult to estimate, especially for $q^2 \sim 4 m_c^2\simeq 6.8$ GeV$^2$. We perform a detailed numerical analysis and present both predictions and results from the fit obtained using most recent data. We find that non-factorizable power corrections of the expected order of magnitude are sufficient to give a good description of current experimental data within the Standard Model. We discuss in detail the $q^2$ dependence of the corrections and their possible interpretation as shifts of the Standard Model Wilson coefficients.