Higgs–photon resonances

Abstract

We study models that produce a Higgs boson plus photon (h0γ) resonance at the LHC. When the resonance is a Z′ boson, decays to h0γ occur at one loop. If the Z′ boson couples at tree level to quarks, then the h0γ branching fraction is typically of order 10 - 5 or smaller. Nevertheless, there are models that would allow the observation of Z′→h0γ at s=13 TeV with a cross section times branching fraction larger than 1 fb for a Z′ mass in the 200–450 GeV range, and larger than 0.1 fb for a mass up to 800 GeV. The one-loop decay of the Z′ into lepton pairs competes with h0γ, even if the Z′ couplings to leptons vanish at tree level. We also present a model in which a Z′ boson decays into a Higgs boson and a pair of collimated photons, mimicking an h0γ resonance. In this model, the h0γ resonance search would be the discovery mode for a Z′ as heavy as 2 TeV. When the resonance is a scalar, although decay to h0γ is forbidden by angular momentum conservation, the h0 plus collimated photons channel is allowed. We comment on prospects of observing an h0γ resonance through different Higgs decays, on constraints from related searches, and on models where h0 is replaced by a nonstandard Higgs boson.