Dark-Photon searches via Higgs-boson production at the LHC

TL;DR

This paper investigates the potential to detect dark photons via Higgs boson decays at the LHC, proposing a model-independent analysis that could reveal dark sector physics with distinctive photon and missing energy signatures.

Contribution

It extends previous studies by analyzing Higgs decays to dark photons at 14 TeV, including realistic background modeling and parton-shower effects, showing feasible detection sensitivities.

Findings

Gluon-fusion channel sensitivity to 0.1% branching ratio with 300 fb^{-1}

VBF channel sensitivity to 1% branching ratio

Model scenarios from unbroken U(1)_F explaining Yukawa hierarchies

Abstract

Dark photons $\bar \gamma$ mediating long-range forces in a dark sector are predicted by various new physics scenarios, and are being intensively searched for in experiments. We extend a previous study of a new discovery process for dark photons proceedings via Higgs-boson production at the LHC. Thanks to the non-decoupling properties of the Higgs boson, BR($H\to \gamma\bar \gamma$) values up to a few percent are possible for a massless dark photon, even for heavy dark-sector scenarios. The corresponding signature consists (for a Higgs boson at rest) of a striking monochromatic photon with energy $E_{\gamma}= m_H/2$, and similar amount of missing energy. We perform a model independent analysis at the LHC of both the gluon-fusion and VBF Higgs production mechanisms at 14 TeV, including parton-shower effects, and updating our previous parton-level analysis at 8 TeV in the gluon-fusion channel by a more realistic background modeling. We find that a $5\sigma$ sensitivity can be reached in the gluon-fusion channel for BR($H\to \gamma\bar \gamma)\simeq\,$0.1% with an integrated luminosity of $L\simeq 300\, {\rm fb}^{-1}$. The corresponding VBF reach is instead restricted to 1%. Such decay rates can be naturally obtained in dark-photon scenarios arising from unbroken $U(1)_F$ models explaining the origin and hierarchy of the Yukawa couplings, strongly motivating the search for this exotic Higgs decay at the LHC.