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

A combination of searches for Higgs boson decays into a visible photon and a massless dark photon (H → γγd) is presented using 139 fb^–1 of proton-proton collision data at a centre-of-mass energy of $\sqrt{\textrm{s}}$ = 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 B(H → γγ_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% confidence level limit on the cross-section times branching ratio ranges from 16 fb (20 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.. Authors: Aad, G. [CPPM, Aix-Marseille Université, CNRS/IN2P3]; Aakvaag, E. [University of Bergen]; Abbott, B. [University of Oklahoma]; Abdelhameed, S. [New York University Abu Dhabi]; Abeling, K. [Georg-August-Universität Göttingen]. DOE Contract: SC0007859. Subjects: 72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS; Hadron-Hadron Scattering; Higgs Physics