Search for the B_s⁰→ μ⁺μ⁻γ decay

A search for the fully reconstructed B_s⁰→ μ⁺μ⁻γ decay is performed at the LHCb experiment using proton-proton collisions at √s = 13 TeV corresponding to an integrated luminosity of 5.4 fb⁻¹. No significant signal is found and upper limits on the branching fraction in intervals of the dimuon mass are set

B(B⁰_s → µ⁺µ⁻γ) < 4.2 × 10⁻⁸, m(µ⁺µ⁻) ∈ [2m_µ, 1.70] GeV/c²,
B(B⁰_s → µ⁺µ⁻γ) < 7.7 × 10⁻⁸, m(µ⁺µ⁻) ∈ [1.70, 2.88] GeV/c²,
B(B⁰_s → µ⁺µ⁻γ) < 4.2 × 10⁻⁸, m(µ⁺µ⁻) ∈ [3.92, m_B0s] GeV/c²,

at 95% confidence level. Additionally, upper limits are set on the branching fraction in the [2m_μ, 1.70] GeV/c² dimuon mass region excluding the contribution from the intermediate ϕ(1020) meson, and in the region combining all dimuon-mass intervals.