Probing CP Violation in $h \to Z\gamma$ with Background Interference

Understand

We show that the parity of the $h Z\gamma$ vertex can be probed by interference between the gluon fusion Higgs production, $gg \to h \to \gamma Z \to \gamma \ell^+\ell^-$, and the background, $gg \to \gamma Z \to \gamma \ell^+\ell^-$, amplitudes.

• In the presence of a parity violating $hZ\gamma$ 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.