Evidence for B-→D**0τ-ντ¯ Decays

The first evidence for the decay B-→D**0τ-ν¯τ 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 D1(2420)0, D2*(2460)0, and D1′(2400)0. The B-→D**0τ-ν¯τ signal is measured with a significance of 3.5σ, including systematic uncertainties. The combined branching fraction B(B-→D1,2**0τ-ν¯τ)×B(D1,2**0→D*+π-), where D1,2**0 denotes both D1(2420)0 and D2*(2460)0 contributions, is measured to be [0.051±0.013(stat)±0.006(syst)±0.009(ext)]%, where the last uncertainty reflects that of the branching fraction of the normalization channel B-→D1,2**0Ds-(*). 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 R(D1,2**0)=0.13±0.03(stat)±0.01(syst)±0.02(ext).