# Probing Lepton Universality with (Semi)-Leptonic B decays

### Submission summary

 As Contributors: Ruben Jaarsma · Gilberto Tetlalmatzi-Xolocotzi Preprint link: scipost_201812_00041v1 Date accepted: 2019-01-17 Date submitted: 2018-12-13 Submitted by: Tetlalmatzi-Xolocotzi, Gilberto Submitted to: SciPost Physics Proceedings Domain(s): Exp. & Theor. Subject area: High-Energy Physics - Phenomenology

### Abstract

The most recent measurements of the observables $R_{D^{(*)}}$ are in tension with the Standard Model offering hints of New Physics in $b\rightarrow c \ell \bar{\nu}_{\ell}$ transitions. Motivated by these results, in this work we present an analysis on their $b\rightarrow u \ell \bar{\nu}_{\ell}$ counterparts (for $\ell=e, ~\mu, ~\tau$). Our study has three main objectives. Firstly, using ratios of branching fractions, we assess the effects of beyond the Standard Model scalar and pseudoscalar particles in leptonic and semileptonic $B$ decays ($B^-\rightarrow \ell^- \bar{\nu}_{\ell}$, $\bar{B}\rightarrow \pi \ell \bar{\nu}_{\ell}$ and $\bar{B}\rightarrow \rho \ell \bar{\nu}_{\ell}$). Here a key role is played by the leptonic $B$ processes, which are highly sensitive to new pseudoscalar interactions. In particular, we take advantage of the most recent measurement of the branching fraction of the channel $B^-\rightarrow \mu^-\bar{\nu}_{\mu}$ by the Belle collaboration. Secondly, we extract the CKM matrix element $|V_{ub}|$ while accounting simultaneously for New Physics contributions. Finally, we provide predictions for the branching fractions of yet unmeasured leptonic and semileptonic $B$ decays.

### Submission & Refereeing History

Submission scipost_201812_00041v1 (13 December 2018)

## Invited Reports on this Submission

Toggle invited reports view

### Greg Ciezarek on 2018-12-23

• Cite as: Greg Ciezarek, Report on arXiv:scipost_201812_00041v1, delivered 2018-12-23, doi: 10.21468/SciPost.Report.767

### Report

This proceeding relates the recent hints of an anomaly in $b \rightarrow c \tau \nu$ processes to current and future measurements in semileptonic $b \rightarrow u \ell \nu$ and fully leptonic $B \rightarrow \ell \nu$ processes.
These measurements can provide important additional information to constrain different interpretations of the b to tau measurements in terms of new physics. This work focuses
on new physics with a (pseudo)scalar Lorentz structure, where it is clearly demonstrated that fully leptonic processes play a greatly enhanced role. Predictions in several new physics scenarios
are presented for quantities which can be measured at ongoing and future experiments. The importance of new measurements distinguishing between decay modes with electrons and muons are emphasized.
This proceeding is an important contribution to the interpretation of tau lepton physics, and is recommended for publication.

• validity: high
• significance: good
• originality: good
• clarity: high
• formatting: good
• grammar: good