Probing CP violation in h →zγ with background interference

We show that the parity of the hZγ vertex can be probed by interference between the gluon fusion Higgs production, gg→h→γZ→γ+-, and the background, gg→γZ→γ+-, amplitudes. In the presence of a parity violating hZγ vertex, this interference alters the kinematic distribution of the leptons and photon compared to Standard Model (SM) expectations. For a Higgs with SM-sized width and couplings, we find that the size of the effect enters at most at the 10-2 level. Such a small effect cannot be seen at the LHC, even with futuristic high luminosities. Should there exist other broader scalar particles with larger production cross-section times branching ratio to Zγ, then the parity structure of their Zγ couplings can be probed with this technique.