Evidence for 𝐵⁻ → 𝐷^**0⁢𝜏⁻⁢𝜈̅_𝜏 Decays

The first evidence for the decay 𝐵⁻→ 𝐷^**0⁢𝜏⁻⁢⁢𝜈̅_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, 𝐷⁢^*₂(2460)⁰, and 𝐷′₁⁢(2400)⁰. The 𝐵⁻ → 𝐷^**0⁢𝜏⁻⁢⁢𝜈̅_𝜏 signal is measured with a significance of 3.5⁢𝜎, including systematic uncertainties. The combined branching fraction ℬ⁡(𝐵⁻ → 𝐷^**0_1,2⁢𝜏⁻⁢𝜈̅_𝜏) × ℬ⁡(𝐷^**0 _1,2 → 𝐷^*+⁢𝜋⁻), where 𝐷^**0_1,2 denotes both 𝐷₁⁢(2420)⁰ and 𝐷^*₂⁢(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⁻ → 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 ℛ⁡(𝐷^**0_1,2) = 0.13 ± 0.03⁢(stat) ± 0.01⁢(syst) ± 0.02⁢(ext).