Search for new physics in semileptonic B-decays

TL;DR

This paper reports measurements of semileptonic B-decays and B_s^0 meson mixing asymmetries, testing the Standard Model and searching for signs of new physics through lepton universality violation and CP asymmetry analysis.

Contribution

It provides the latest experimental results on semileptonic B-decays and B_s^0 mixing asymmetries, including a measurement of R(D*) and CP asymmetry, with implications for physics beyond the Standard Model.

Findings

R(D*)) is 2.1 sigma above SM expectation

CP asymmetry in B_s^0 mixing is consistent with SM

Results constrain new physics models

Abstract

Semileptonic decays provide an excellent environment for testing the Standard Model (SM). Violation of lepton universality would be a smoking gun for physics beyond the SM. Using semi-tauonic $B$ decays, LHCb finds a value of $\mathcal{R}(D^*) = \mathcal{B}(\bar{B}^0 \to D^{*+} \tau^{-} \bar{\nu}_{\tau})/\mathcal{B}(\bar{B}^0 \to D^{*+} \mu^{-} \bar{\nu}_{\mu}) = 0.336 \pm 0.027 \rm{(stat)} \pm 0.030 \rm{(syst)}$, which is 2.1 standard deviations larger than the value expected from the SM. Moreover, the measurement of the $CP$ asymmetry in mixing of $B_s^0$ mesons is highly sensitive to physics beyond the SM. This article presents the latest result on semileptonic asymmetries; using the full Run 1 dataset, it is found that $a_{\rm{sl}}^s = (0.39 \pm 0.26 \rm{(stat)} \pm 0.20 \rm{(syst)})\%$, which is consistent with the Standard Model.