UC Riverside

This thesis presents an on-going search for self-interacting dark matter from events with two displaced

lepton-jets in the CMS detector with pp collision data taken at $\sqrt{s}=13\TeV$ corresponding

to 59.74 $\text{fb}^{-1}$ of integrated luminosity during Run 2 of the LHC. Lepton-jet is a group

of collimated leptons in a narrow cone, which can be the signature of dark photon $Z_d$ --

a theorized gauge boson which is charged under U(1)$_d$ gauge symmetry, bridging the dark sector

and the Standard Model. As the first-round analysis, this search focuses more on displaced dark photons decaying to muon pair

or electron pair. The expected results are presented as 95\% confidence level upper limits on the

self-interacting dark matter bound state production cross section, assuming the branch fraction

of the bound state to dark photon pair is 100\%.