Interference Effects in 𝐠𝐠 → 𝐇 → 𝐙 γ Beyond Leading Order

The ATLAS and CMS collaborations at the LHC have recently announced evidence for the rare Higgs boson decay into a Z boson and a photon. We analyze the interference between the process gg→ H → Z γ induced by loops of heavy particles, which is by far the dominant contribution to the signal, and the continuum gg → Z γ QCD background process mediated by light quark loops. This interference modifies the event yield, the resonance line-shape and the apparent mass of the Higgs boson. We calculate the radiative corrections to this interference beyond the leading-order approximation in perturbative QCD and find that, while differing numerically from the corresponding effects on the more studied gg →γγ signal, they are generally rather small. As such, they do not impact significantly the interpretation of the present measurements of the H → Z γ decay mode.