Soft displaced leptons at the LHC
Freya Blekman, Nishita Desai, et al.
Soft displaced leptons are representative collider signatures of compressed dark sectors with feeble couplings to the standard model. A prime target are dark matter scenarios where co-scattering or co-annihilation sets the relic abundance upon freeze-out. At the LHC, searches for soft displaced leptons are challenged by a large background from hadron or tau lepton decays. In this article, we present an analysis tailored for displaced leptons with a low transverse momentum threshold at 20 GeV. Using a neural network, we perform a comprehensive analysis of the event kinematics, including a study of the expected detection efficiencies and backgrounds at small momenta. Our results show that weak-scale mediators to a compressed dark sector with decay lengths between 1 mm and 1 m can be probed with LHC Run 2 data. This motivates the design of dedicated triggers that maximize the sensitivity to displaced soft leptons.