Lepton Jets from Radiating Dark Matter

TL;DR

This paper explores how lepton jets can serve as signals of an extended dark sector with radiating dark photons, analyzing their production, decay, and detection prospects at the LHC through simulations and recasting existing searches.

Contribution

It introduces a detailed analysis of dark photon radiation from dark matter at the LHC, deriving energy spectra and simulating lepton jet signatures to constrain dark sector models.

Findings

Recast ATLAS lepton jet searches to constrain dark sector parameters.

Derived dark photon energy spectrum analytically and via simulations.

Projected future LHC sensitivities to radiating dark matter models.

Abstract

The idea that dark matter forms part of a larger dark sector is very intriguing, given the high degree of complexity of the visible sector. In this paper, we discuss lepton jets as a promising signature of an extended dark sector. As a simple toy model, we consider an $\mathcal{O}(\text{GeV})$ DM fermion coupled to a new $U(1)'$ gauge boson (dark photon) with a mass of order GeV and kinetically mixed with the Standard Model photon. Dark matter production at the LHC in this model is typically accompanied by collinear radiation of dark photons whose decay products can form lepton jets. We analyze the dynamics of collinear dark photon emission both analytically and numerically. In particular, we derive the dark photon energy spectrum using recursive analytic expressions, using Monte Carlo simulations in Pythia, and using an inverse Mellin transform to obtain the spectrum from its moments. In the second part of the paper, we simulate the expected lepton jet signatures from radiating dark matter at the LHC, carefully taking into account the various dark photon decay modes and allowing for both prompt and displaced decays. Using these simulations, we recast two existing ATLAS lepton jet searches to significantly restrict the parameter space of extended dark sector models, and we compute the expected sensitivity of future LHC searches.