A new tool to search for physics beyond the Standard Model in $\overline{B}\to D^{\ast +}{\ell }^{-}\overline{\nu }$

arXiv

2203.07189

Date

2022-03-14

Frontier

Rare Processes and Precision Frontier (RF)

Topical groups

• RF1

Submitted by

Bhuabnjyoti Bhattacharya

Abstract

Recent experimental results in $B$ physics from Belle, BaBar and LHCb suggest new physics (NP) in the weak $b\to c$ charged-current and the $b\to s$ neutral-current processes. Here we focus on the charged-current case and specifically on the decay modes $B\to D^{\ast +}{\ell }^{-}\overline{\nu }$ with $\ell =e,\mu ,$ and $\tau$. The world averages of the ratios $R_D$ and $R_D^{\ast }$ currently differ from the Standard Model (SM) by $3.4\sigma$ while $\mathrm{\Delta }{A}_{FB}=A_{FB}(B\to D^{\ast }\mu \nu )-A_{FB}(B\to D^{\ast }e\nu )$ is found to be $4.1\sigma$ away from the SM prediction in an analysis of 2019 Belle data. These intriguing results suggest an urgent need for improved simulation and analysis techniques in $B\to D^{\ast +}{\ell }^{-}\overline{\nu }$ decays. Here we describe a Monte Carlo Event-generator tool based on EVTGEN developed to allow simulation of the NP signatures in $B\to D^{\ast }{\ell }^{-}\nu$, which arise due to the interference between the SM and NP amplitudes. As a demonstration of the proposed approach, we exhibit some examples of NP couplings that are consistent with current data and could explain the $\mathrm{\Delta }{A}_{FB}$ anomaly in $B\to D^{\ast }{\ell }^{-}\nu$ while remaining consistent with other constraints. We show that the $\mathrm{\Delta }$-type observables such as $\mathrm{\Delta }{A}_{FB}$ and $\mathrm{\Delta }{S}_5$ eliminate most QCD uncertainties from form factors and allow for clean measurements of NP. We introduce correlated observables that improve the sensitivity to NP. We discuss prospects for improved observables sensitive to NP couplings with the expected 50 ab${}^{-1}$ of Belle II data, which seems to be ideally suited for this class of measurements.