Search for self-interacting dark matter

We introduce a new search for self-interacting dark matter produced in proton-proton collisions at the Large Hadron Collider (LHC). In the considered model, pair-produced dark matter particles form a bound state that decays into a pair of boosted dark photons, which each decay into charged leptons via a kinetic mixing portal. The resulting signature is a pair of displaced and highly collimated back-to-back lepton pairs, which we reconstruct as a lepton jet (LJ). Specifically we consider the case when one dark photon decays to two muons while the second decay to either muons or electrons. Double muon triggers are used to select events from the CMS experiment's 2018 data. No vertex requirements are applied due to the displaced decays. We present the strategy for the LJ reconstruction, the reconstruction and trigger efficiency as well as collimation studies using MC simulated samples.