Insights on the current semi-leptonic B-decay discrepancies — and how Bs → μ+μ−γ can help
Diego Guadagnoli, C. Normand, Silvano Simula, Ludovico Vittorio
Abstract
A bstract B s → μ + μ − γ , measured at high q 2 as a partially reconstructed decay, can probe the origin of the existing discrepancies in semi-leptonic b → s and b → c decays. We perform a complete study of this possibility. We start by reassessing the alleged discrepancies, with a focus on a unified EFT description. Using the SMEFT, we find that the tauonic Wilson coefficient required by R ( D (*) ) implies a universal muonic Wilson coefficient of precisely the size required by semi-muonic BR data and, separately, by semi-muonic angular analyses. We thus identify reference scenarios. Importantly, B s → μ + μ − γ offers a strategy to access them without being affected by the long-distance issues that hamper the prediction of semi-leptonic B decays at low q 2 . After quantifying to the best of our knowledge the B s → μ + μ − γ experimental over the long haul, we infer the B s → μ + μ − γ sensitivity to the couplings relevant to the anomalies. In the example of the real- δC 9 , 10 scenario, we find significances below 3 σ . Such figure is to be compared with other single -observable sensitivities that one can expect from e.g. BR and angular data, whether at low or high q 2 , and not affected by long-distance issues such as narrow resonances or intermediate charmed di-meson rescattering.