Dark photon searches via Higgs boson production at the LHC and beyond

TL;DR

This paper explores the potential of Higgs boson decays into a photon and a massless dark photon as a promising method to detect dark photons at colliders, highlighting its insensitivity to high-energy UV scales and reviewing current experimental bounds.

Contribution

It introduces a novel Higgs-mediated production mechanism for dark photons that is less dependent on UV physics and reviews experimental constraints from the LHC and future collider prospects.

Findings

Higgs decay into photon and dark photon produces a distinctive monochromatic photon signature.

Current LHC bounds from CMS and ATLAS constrain the Higgs to dark photon decay channel.

Future $e^+e^-$ colliders could improve sensitivity to dark photon production via Higgs processes.

Abstract

Many scenarios beyond the standard model, aiming to solve long-standing cosmological and particle physics problems, suggest that dark matter might experience long-distance interactions mediated by an unbroken dark $U(1)$ gauge symmetry, hence foreseeing the existence of a massless dark photon. Contrary to the massive dark photon, a massless dark photon can only couple to the standard model sector by means of effective higher dimensional operators. Massless dark-photon production at colliders will then in general be suppressed at low energy by a UV energy scale, which is of the order of the masses of portal (messenger) fields connecting the dark and the observable sectors. A violation of this expectation is provided by dark-photon production mediated by the Higgs boson, thanks to the non-decoupling Higgs properties. Higgs-boson production at colliders, followed by the Higgs decay into a photon and a dark photon, provides then a very promising production mechanism for the dark photon discovery, being insensitive in particular regimes to the UV scale of the new physics. This decay channel gives rise to a peculiar signature characterized by a monochromatic photon with energy half the Higgs mass (in the Higgs rest frame) plus missing energy. We show how such resonant photon-plus-missing-energy signature can uniquely be connected to a dark photon production. Higgs boson production and decay into a photon and a dark photon as a source of dark photons is reviewed at the Large Hadron Collider, in the light of the present bounds on the corresponding signature by the CMS and ATLAS collaborations. Perspectives for the dark-photon production in Higgs-mediated processes at future $e^+e^-$ colliders are also discussed.