Background processes in Higgs decay to Z gamma

The ATLAS and CMS Collaborations reported that the observed number of Higgs boson decays into a $Z$ boson and a photon is $\mu = 2.2 \pm 0.7$ times higher than predicted by the Standard Model. Initially, this discrepancy was attributed to a modification of the $HZ\gamma$ vertex. In the $H \to Z\gamma$ process, this decay is reconstructed from $H \to \ell\ell\gamma$, where $\ell$ represents either an electron or a muon. In this study, an investigation is conducted to examine this anomaly by exploring potential additional background contributions to $H \to \ell\ell\gamma$ from various subprocesses within and beyond the Standard Model.