Konstantinidis, Nikolaos; ATLAS Collaboration, Collaboration; (2023) Searches for exclusive Higgs and Z boson decays into a vector quarkonium state and a photon using 139 fb^{-1} of ATLAS \sqrt{s}=13 TeV proton–proton collision data. European Physical Journal C: Particles and Fields , 83 , Article 781. 10.1140/epjc/s10052-023-11869-1.

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Abstract

Searches for the exclusive decays of Higgs and Z bosons into a vector quarkonium state and a photon are performed in the \mu ^+\mu ^-\,\gamma final state with a proton–proton collision data sample corresponding to an integrated luminosity of 139 fb^{-1} collected at \sqrt{s}=13 TeV with the ATLAS detector at the CERN Large Hadron Collider. The observed data are compatible with the expected backgrounds. The 95% confidence-level upper limits on the branching fractions of the Higgs boson decays into J/\psi \,\gamma, \psi (2S)\,\gamma, and \Upsilon (1S,2S,3S)\,\gamma are found to be 2.0\times 10^{-4}, 10.5\times 10^{-4}, and (2.5,4.2,3.4)\times 10^{-4}, respectively, assuming Standard Model production of the Higgs boson. The corresponding 95% CL upper limits on the branching fractions of the Z boson decays are 1.2\times 10^{-6}, 2.4\times 10^{-6}, and (1.1,1.3,2.4)\times 10^{-6}. An observed 95% CL interval of (-133,175) is obtained for the \kappa _c/\kappa _\gamma ratio of Higgs boson coupling modifiers, and a 95% CL interval of (-37,40) is obtained for \kappa _b/\kappa _\gamma.

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