Exploring Background Contributions in $H\to Z{\hat{I}}^3$ Decay

Abstract

The rare decay $H\to Z{\hat{I}}^3$ has been investigated by both the ATLAS and CMS Collaborations, with each reporting an excess in Run~2 in 2023 characterized by $\hat{I}¼=2.2\pm 0.7$. This anomaly was initially attributed to possible modifications of the $HZ{\hat{I}}^3$ vertex. However, because the $H\to Z{\hat{I}}^3$ signal is reconstructed via the $H\to \ell \ell {\hat{I}}^3$ channel, background effects -- particularly those from processes that mimic the same final state -- may have been underestimated. In this work, we re-examine these backgrounds in detail and propose that the observed excess could be explained by an additional BSM-induced contribution. We present both an effective field theory framework and a UV-complete model that provide the necessary rates and a consistent interpretation of the data. The proposed model reproduces the newest ATLAS result, $\hat{I}¼=1.3_{-0.5}^{+0.6}$, obtained using a narrower dilepton invariant-mass window.

10 pages, 3 figures, 1 table, proceedings to European Physical Society Conference on High Energy Physics