Higgs boson decay into a lepton pair and a photon: A roadmap to the discovery of H → Zγ and probes of new physics

The decay H -> l(+)l(-) gamma, l = e, mu receives contributions from H -> Z[-> l(+) l(-)]gamma and a nonresonant contribution, both of which are loop induced. We describe how one can separate these subprocesses in a gauge-independent way, define the decay rate Gamma(H -> Z gamma), and extract the latter from differential H -> l(+)l(-)gamma branching ratios. For l = mu, also the tree decay rate, which is driven by the muon Yukawa coupling, is important. We propose kinematic cuts optimized to separate the three contributions, paving the way to the milestone (i) discovery of H -> Z gamma, (ii) discovery of H -> mu(+)mu(-)gamma vertical bar(tree), and (iii) quantification of new physics in both the effective H-Z-gamma and nonresonant H-l(+)-l(-)-gamma couplings.

Automated summary

This paper discusses the decay process of H -> l(+)l(-) gamma, including the contributions from H -> Z[-> l(+) l(-)]gamma and nonresonant processes. We propose a gauge-independent method to separate these decay processes and define the decay rate Gamma(H -> Z gamma). By extracting the necessary decay processes from differential branching ratios, we can quantify the tree decay rate driven by the muon Yukawa coupling for l = mu. We propose optimized kinematic cuts to separate the three contributions, paving the way for the discovery of H -> Z gamma, the discovery of H -> mu(+)mu(-)gamma |(tree), and the quantification of new physics in both the effective H-Z-gamma and nonresonant H-l(+)-l(-)-gamma couplings.