Z boson radiative decay Z → μ+μ−γ at the LHC

A bstract We study the radiative decay of the Z boson, Z → μ + μ − γ , at the LHC, providing both Standard Model (SM) precision analysis and new physics projections. With detailed analysis of Run-2 and future HL-LHC performances, we demonstrate that this decay mode can be measured with a statistical precision at the sub-percentage level. From existing Run-1 data, we extract Br fid ( Z → μμγ ) = (3 . 34 ± 0 . 016) × 10 − 4 . We further explore the sensitivity of this channel to axion-like particles (ALPs) and to an anomalous U (1) X gauge boson coupled to the muon. Both scenarios feature resonant structures in the dimuon invariant mass spectrum within the Z → a/X + γ → μ + μ − γ final state. Our results show that the radiative Z decay provides a clean and statistically powerful probe of such leptophilic new physics, extending the current collider reach for ALPs and anomalous gauge forces down to g X ~ 𝒪(10 − 3 ). This study highlights the potential of rare electroweak gauge boson decays as precision tests of the SM and sensitive probes of new interactions at the LHC.