Search for Higgs boson decays to a Z boson and a photon in proton-proton collisions at $\sqrt{s}$ = 13 TeV



Results are presented from a search for the Higgs boson decay $\mathrm{H}\to\mathrm{Z}\gamma$, where $\mathrm{Z}\to\ell^+\ell^-$ with $\ell=\mathrm{e}$ or $\mu$. The search is performed using a sample of proton-proton ($\mathrm{pp}$) collision data at a center-of-mass energy of $13~\mathrm{TeV}$, recorded by the CMS experiment at the LHC, corresponding to an integrated luminosity of $138~\mathrm{fb}^{-1}$. Events are assigned to mutually exclusive categories, which exploit differences in both event topology and kinematics of distinct Higgs production mechanisms to enhance signal sensitivity. The signal strength $\mu$, defined as the product of the cross section and the branching fraction [$\sigma(\mathrm{pp}\to\mathrm{H})\mathcal{B}(\mathrm{H}\to\mathrm{Z}\gamma)$] relative to the standard model prediction, is extracted from a simultaneous fit to the \llg invariant mass distributions in all categories and is found to be $\mu= 2.4\pm0.9$ for a Higgs boson mass of $125.38~\mathrm{GeV}$. The statistical significance of the observed excess of events is 2.7 standard deviations. This measurement corresponds to $\sigma(\mathrm{pp}\to\mathrm{H})\mathcal{B}(\mathrm{H}\to\mathrm{Z}\gamma)=0.21\pm0.08~\mathrm{pb}$. The observed (expected) upper limit at 95% confidence level on $\mu$ is $4.1$ ($1.8$). The ratio of branching fractions $\mathcal{B}(\mathrm{H}\to\mathrm{Z}\gamma)/\mathcal{B}(\mathrm{H}\to\gamma\gamma)$ is measured to be $1.5^{+0.7}_{-0.6}$, which agrees with the standard model prediction of $0.69 \pm 0.04$ at the 1.5 standard deviation level.
Date made available29 Apr 2022


  • hep-ex


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