First Evidence of the B_{s}^{0}→K^{-}π^{+}γ Decay

Area of Science:

• Particle Physics
• High Energy Physics
• Quantum Chromodynamics

Background:

• The B_{s}^{0}→K^{-}π^{+}γ decay is a rare B-meson decay.
• Previous searches had not established experimental evidence for this decay mode.

Purpose of the Study:

• To perform the first search for the B_{s}^{0}→K^{-}π^{+}γ decay.
• To measure the ratio of branching fractions for this decay relative to the favored B[over ¯]^{0}→K^{-}π^{+}γ decay.

Main Methods:

• Utilized proton-proton collision data from the LHCb experiment at 7, 8, and 13 TeV.
• Reconstructed photons via electron-positron pair conversion for improved mass resolution.
• Analyzed the invariant mass spectrum of K^{-}π^{+} pairs in the range 796-1800 MeV/c².

Main Results:

• Observed a signal excess with 3.5 standard deviations significance, providing the first experimental evidence for B_{s}^{0}→K^{-}π^{+}γ.
• Measured the ratio R=(3.7±1.2±0.4)×10^{-2} in the 796-996 MeV/c² range, consistent with the Standard Model.
• Measured R=(0.2±2.7±1.3)×10^{-2} in the 996-1800 MeV/c² range.

Conclusions:

• Established the first experimental evidence for the B_{s}^{0}→K^{-}π^{+}γ decay.
• The measured branching fraction ratios are consistent with Standard Model predictions.
• The improved mass resolution from photon conversion aids in precise measurements of rare decays.