Measurement of the ratio of branching fractions $\mathcal{B}(\overline{B}^0 \to D^{*+}\tau^{-}\overline{\nu}_{\tau})/\mathcal{B}(\overline{B}^0 \to D^{*+}\mu^{-}\overline{\nu}_{\mu})$

TL;DR

This paper reports the first measurement of the ratio of branching fractions for B meson decays involving tau and muon leptons at a hadron collider, providing insights into potential new physics beyond the Standard Model.

Contribution

The study presents the first measurement of the branching ratio of B meson decays involving tau leptons at a hadron collider, using LHCb data from 2011-2012.

Findings

Measured ratio $ (D^*)$ = 0.336 ± 0.027 (stat) ± 0.030 (syst)

Result is 2.1 standard deviations above the Standard Model expectation

First such measurement at a hadron collider

Abstract

The branching fraction ratio $\mathcal{R}(D^{*}) \equiv \mathcal{B}(\overline{B}^0 \to D^{*+}\tau^{-}\overline{\nu}_{\tau})/\mathcal{B}(\overline{B}^0 \to D^{*+}\mu^{-}\overline{\nu}_{\mu})$ is measured using a sample of proton-proton collision data corresponding to 3.0\invfb of integrated luminosity recorded by the LHCb experiment during 2011 and 2012. The tau lepton is identified in the decay mode $\tau^{-} \to \mu^{-}\overline{\nu}_{\mu}\nu_{\tau}$. The semitauonic decay is sensitive to contributions from non-Standard-Model particles that preferentially couple to the third generation of fermions, in particular Higgs-like charged scalars. A multidimensional fit to kinematic distributions of the candidate $\overline{B}^0$ decays gives $\mathcal{R}(D^{*}) = 0.336 \pm 0.027(stat) \pm 0.030 (syst)$. This result, which is the first measurement of this quantity at a hadron collider, is 2.1 standard deviations larger than the value expected from lepton universality in the Standard Model.