Evidence for $B^-\rightarrow D^{**0}\tau^-\overline{\nu_{\tau}}$ decays

TL;DR

This paper reports the first evidence for the decay of B- mesons into excited charm mesons and tau neutrinos, using LHCb data, with a significance of 3.5 sigma and measurements of branching fractions and decay ratios.

Contribution

It provides the first experimental evidence for the decay mode B- to D**0 tau nu, expanding understanding of semileptonic B decays involving tau leptons.

Findings

First evidence for B- to D**0 tau nu decay at 3.5 sigma significance.

Measured combined branching fraction: (0.051 ± 0.013 (stat) ± 0.006 (syst) ± 0.009 (ext))%.

Determined the ratio R(D**0_{1,2}) = 0.13 ± 0.03 (stat) ± 0.01 (syst) ± 0.02 (ext).

Abstract

The first evidence for the decay $B^-\rightarrow D^{**0}\tau^-\overline{\nu_{\tau}}$ is obtained using proton-proton collision data collected by the LHCb experiment, corresponding to an integrated luminosity of 9 fb$^{-1}$ , at centre-of-mass energies of 7, 8 and 13 Tev. Here, the $D^{**0}$ meson represents any of the three excited charm mesons $D_{1}(2420)^{0}$, $D_{2}^{*}(2460)^{0}$, and $D_{1}^{'}(2400)^{0}$. The $B^-\rightarrow D^{**0}\tau^-\overline{\nu_{\tau}}$ signal is measured with a significance of 3.5 $\sigma$, including systematic uncertainties. The combined branching fraction $BR(B^-\rightarrow D^{**0}_{1,2}\tau^-\overline{\nu_{\tau}})\times BR(D^{**0}_{1,2}\rightarrow D^{*+}\pi^-)$, where $D^{**0}_{1,2}$ denotes both $D_{1}(2420)^{0}$ and $D_{2}^{*}(2460)^{0}$ contributions, is measured to be $(0.051\pm0.013(stat)\pm 0.006(syst)\pm 0.009(\rm{ext}) )\%$, where the last uncertainty reflects that of the branching fraction of the normalisation channel $B^-\rightarrow D^{**0}_{1,2}D_s^{(*)-}$. The ratio between the tauonic and muonic semileptonic $B$ decays, with the latter taken from world average values, is also determined and found to be ${\cal R}(D^{**0}_{1,2})=0.13\pm0.03(stat)\pm0.01(syst)\pm0.02\,(\rm{ext})$.