Combination of searches for Higgs boson decays into a photon and a massless dark photon using $pp$ collisions at $\sqrt{s} = 13$ TeV with the ATLAS detector

TL;DR

This paper combines multiple searches for Higgs decays into a photon and a massless dark photon using ATLAS data, setting upper limits on the decay rate and exploring higher-mass Higgs bosons.

Contribution

It provides the first combined analysis of Higgs to photon plus dark photon decays at 13 TeV, setting new upper limits and extending sensitivity to higher Higgs masses.

Findings

95 ext% CL upper limit on Higgs decay branching ratio is 1.3%

Limits on cross section times branching ratio range from 16 fb to 1.0 fb

Analysis extends sensitivity to Higgs masses up to 3 TeV

Abstract

A combination of searches for Higgs boson decaying into a visible photon and a massless dark photon ($H\to\gamma\gamma_{\text{d}}$) is presented using 139 fb$^{-1}$ of proton--proton collision data at a centre-of-mass energy of $\sqrt{s} = 13$ TeV recorded by the ATLAS detector at the Large Hadron Collider. The observed (expected) 95\% confidence level upper limit on the Standard Model Higgs boson decay branching ratio is determined to be $\mathcal{B}(H\to\gamma\gamma_{\text{d}}) < $ 1.3% (1.5)%. The search is also sensitive to higher-mass Higgs bosons decaying into the same final state. The observed (expected) 95% CL limit on the cross section times branching ratio ranges from 16 fb (26 fb) for $m_H = 400$ GeV to 1.0 fb (1.5 fb) for $m_H = 3$ TeV. Results are also interpreted in the context of a minimal simplified model.