Zooming in on $B\to K^\ast \ell\ell$ decays at low recoil

TL;DR

This paper analyzes $B\to K^* \ell\ell$ decays at low recoil using an operator product expansion and charm contribution models, finding current data consistent with the Standard Model but allowing for potential new physics.

Contribution

It introduces a data-driven, model-independent approach to assess the limitations of the OPE in $B\to K^* \ell\ell$ decays at low recoil, incorporating charm effects.

Findings

Current fits show small sensitivity to charm models.

Results are consistent with the Standard Model.

Room remains for new physics signals.

Abstract

We analyse $B\to K^\ast \ell\ell$ decays in the region of low hadronic recoil, where an operator product expansion (OPE) in $1/m_b$ applies. Using a local model for charm contributions based on $e^+ e^- \to hadrons$ against the OPE provides a data-driven method to access the limitations to the OPE's accuracy related to binnings in the dilepton mass. Model-independent fits to $B\to K^\ast \mu \mu $ low recoil angular observables exhibit presently only small sensitivity to different charm models. They give similar results as the fits based on the OPE, and are in agreement with the standard model, but leave also room for new physics. Measurements with resolution small enough to probe charm resonances would be desirable.