Implications from clean observables for the binned analysis of B -> K*ll at large recoil

TL;DR

This paper analyzes q^2-dependent angular observables in B->K*ll decays at large recoil, emphasizing the importance of clean observables with limited form factor dependence for detecting New Physics, supported by Standard Model predictions and recent LHCb data.

Contribution

It identifies optimal observables for New Physics searches in B->K*ll decays, highlighting the role of q^2-binning and providing semi-numerical expressions for these observables.

Findings

Certain P_i observables are less sensitive to soft form factors.

Comparison of Standard Model predictions with LHCb data.

Identification of New Physics benchmark points.

Abstract

We perform a frequentist analysis of q^2-dependent B-> K*(->Kpi)ll angular observables at large recoil, aiming at bridging the gap between current theoretical analyses and the actual experimental measurements. We focus on the most appropriate set of observables to measure and on the role of the q^2-binning. We highlight the importance of the observables P_i exhibiting a limited sensitivity to soft form factors for the search for New Physics contributions. We compute predictions for these binned observables in the Standard Model, and we compare them with their experimental determination extracted from recent LHCb data. Analyzing b->s and b->sll transitions within four different New Physics scenarios, we identify several New Physics benchmark points which can be discriminated through the measurement of P_i observables with a fine q^2-binning. We emphasise the importance (and risks) of using observables with (un)suppressed dependence on soft form factors for the search of New Physics, which we illustrate by the different size of hadronic uncertainties attached to two related observables (P_1 and S_3). We illustrate how the q^2-dependent angular observables measured in several bins can help to unravel New Physics contributions to B-> K*(->Kpi)ll, and show the extraordinary constraining power that the clean observables will have in the near future. We provide semi-numerical expressions for these observables as functions of the relevant Wilson coefficients at the low scale.