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

Abstract

Results are presented from a search for the Higgs boson decay H $\to$ Z$\gamma$, where Z $\to$ ${\ell }^{+}{\ell }^{-}$ with $\ell$ = e or $\mu$. The search is performed using a sample of proton-proton (pp) collision data at a center-of-mass energy of 13 TeV, recorded by the CMS experiment at the LHC, corresponding to an integrated luminosity of 138 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 [$\sigma ($pp $\to$ H$)\mathcal{B}($H $\to$ Z$\gamma )$] relative to the standard model prediction, is extracted from a simultaneous fit to the ${\ell }^{+}{\ell }^{-}\gamma$ invariant mass distributions in all categories and is found to be $\mu$ = 2.4 $\pm$ 0.9 for a Higgs boson mass of 125.38 GeV. The statistical significance of the observed excess of events is 2.7 standard deviations. This measurement corresponds to $\sigma ($pp $\to$ H$)\mathcal{B}($H $\to$ Z$\gamma )$ = 0.21 $\pm$ 0.08 pb. The observed (expected) upper limit at 95% confidence level on $\mu$ is 4.1 (1.8). The ratio of branching fractions $\mathcal{B}($H $\to$ Z$\gamma )/\mathcal{B}($H $\to$ $\gamma \gamma )$ is measured to be 1.5 ${}_{-0.6}^{+0.7}$, which agrees with the standard model prediction of 0.69 $\pm$ 0.04 at the 1.5 standard deviation level.

Replaced with the published version. Added the journal reference and the DOI. All the figures and tables can be found at http://cms-results.web.cern.ch/cms-results/public-results/publications/HIG-19-014 (CMS Public Pages)

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