Search for the rare Higgs boson decay H $\to$ Z$\gamma$ in proton-proton collisions at $\sqrt{s}$ = 13 and 13.6 TeV

Abstract

A search is presented for the rare, loop-induced Higgs boson decay H $\to$ Z$\gamma$, where Z $\to$ $\ell^+\ell^-$ and $\ell$ = e or $\mu$. The search is performed using a sample of proton-proton (pp) collision data at the center-of-mass energies of 13 and 13.6 TeV, recorded by the CMS experiment at the LHC and corresponding to a total integrated luminosity of 200 fb$^{-1}$. The analysis design separately considers and optimizes sensitivity to Higgs boson production via gluon-gluon fusion, vector boson fusion, and associated-production processes. The signal is extracted from a simultaneous fit to the invariant mass distributions of the $\ell^+\ell^-\gamma$ system in the various production channels and event categories. The observed (expected) signal strength $\mu$, defined as the ratio of the measured product the of cross section and decay branching fraction value $\sigma$(pp $\to$ H)$\mathcal{B}$(H $\to$ Z$\gamma$) to the corresponding value predicted in the standard model, is found to be $\mu$ = 1.10$^{+0.52}_{-0.61}$ (1.00$^{+0.49}_{-0.46}$) for a Higgs boson mass of 125.38 GeV. The signal has an observed (expected) significance of 1.9 (2.3) standard deviations.