First Evidence of the 𝐵0𝑠→𝐾−⁢𝜋+⁢𝛾 Decay

The first search for the 𝐵0𝑠→𝐾−⁢𝜋+⁢𝛾 decay in the range 796<𝑚⁡(𝐾−⁢𝜋+)<1800  MeV/𝑐2
is performed using data from proton-proton collisions collected by the LHCb experiment at center-of-mass energies of 7, 8, and 13 TeV, corresponding to an integrated luminosity of 9  fb−1. The photons are reconstructed through their conversion into an electron-positron pair, which significantly improves the mass resolution of the reconstructed decays with respect to decays with an unconverted photon. A signal excess with a significance of 3.5 standard deviations is measured, constituting the first experimental evidence for this decay. In the range 796<𝑚⁡(𝐾−⁢𝜋+)<996  MeV/𝑐2, the ratio ℛ between the branching fractions of the signal decay and the favored ‾‾‾ 𝐵0→𝐾−⁢𝜋+⁢𝛾 decay is measured to be ℛ=(3.7±1.2±0.4)×10−2
where the first uncertainty is statistical and the second is systematic. This measurement is consistent with the value predicted in the Standard Model. In the range 996<𝑚⁡(𝐾−⁢𝜋+)<1800  MeV/𝑐2, the ratio ℛ=(0.2±2.7±1.3)×10−2 is measured.