Search for dark photons in Higgs boson production via vector boson fusion in proton-proton collisions at $\sqrt{s} =$ 13 TeV

TL;DR

This paper reports a search for Higgs boson decays into a dark photon and an undetected particle via vector boson fusion at 13 TeV, setting upper limits on the branching fraction with no significant excess observed.

Contribution

First search for Higgs decays to dark photons in vector boson fusion channel at the LHC, providing new constraints on such models.

Findings

No significant excess observed above background.

Upper limit on Higgs to dark photon decay branching fraction is 3.5% at 125 GeV.

Combined analysis with previous Z-associated production limits the branching fraction to 2.9%.

Abstract

A search is presented for a Higgs boson that is produced via vector boson fusion and that decays to an undetected particle and an isolated photon. The search is performed by the CMS Collaboration at the LHC, using a data set corresponding to an integrated luminosity of 130 fb$^{-1}$, recorded at a center-of-mass energy of 13 TeV in 2016-2018. No significant excess of events above the expectation from the standard model background is found. The results are interpreted in the context of a theoretical model in which the undetected particle is a massless dark photon. An upper limit is set on the product of the cross section for production via vector boson fusion and the branching fraction for such a Higgs boson decay, as a function of the Higgs boson mass. For a Higgs boson mass of 125 GeV, assuming the standard model production rates, the observed (expected) 95% confidence level upper limit on the branching fraction is 3.5 (2.8)%. This is the first search for such decays in the vector boson fusion channel. Combination with a previous search for Higgs bosons produced in association with a Z boson results in an observed (expected) upper limit on the branching fraction of 2.9 (2.1)% at 95% confidence level.