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Probing Lepton Universality with (Semi)-Leptonic B decays

by Giovanni Banelli, Robert Fleischer, Ruben Jaarsma and Gilberto Tetlalmatzi-Xolocotzi

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Submission summary

Authors (as registered SciPost users): Ruben Jaarsma · Gilberto Tetlalmatzi-Xolocotzi
Submission information
Preprint Link: scipost_201812_00041v1  (pdf)
Date accepted: 2019-01-17
Date submitted: 2018-12-13 01:00
Submitted by: Tetlalmatzi-Xolocotzi, Gilberto
Submitted to: SciPost Physics Proceedings
Proceedings issue: The 15th International Workshop on Tau Lepton Physics (TAU2018)
Ontological classification
Academic field: Physics
  • High-Energy Physics - Theory
  • High-Energy Physics - Phenomenology
Approaches: Experimental, Theoretical


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.

Published as SciPost Phys. Proc. 1, 013 (2019)

Reports on this Submission

Report 1 by Greg Ciezarek on 2018-12-23 (Invited Report)

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


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

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