Search for the radiative Ξb− → Ξ ⁻ γ decay

The first search for the rare radiative decay Ξb− → Ξ⁻γ is performed using data collected by the LHCb experiment in proton-proton collisions at a center-of-mass energy of 13 TeV, corresponding to an integrated luminosity of 5.4 fb⁻¹. The Ξb− → Ξ⁻J/ψ channel is used as normalization. No Ξb− → Ξ⁻γ signal is found and an upper limit of B(Ξb− → Ξ⁻γ) < 1.3 × 10⁻⁴ at 95% confidence level is obtained. [Figure not available: see fulltext.]