Search for emerging-jet signatures in pp collisions at 13 TeV with CMS using a fully data-based method for background extraction

Abstract

For this thesis, I present a search for emerging jets produced in proton-proton collisions at a center-of-mass energy of 13 TeV. This search examines a hypothetical dark QCD sector that couples to the standard model through a scalar mediator. The scalar mediator decays into a standard model quark and a dark sector quark. As the dark sector quark showers and hadronizes, it produces long-lived dark mesons that subsequently decay into SM particles, resulting in a jet with multiple displaced vertices, known as an emerging jet. This search extends the existing efforts of CMS by including the possibility of a flavored coupling between the standard model sector and dark sector, which results in emerging jets containing both long-lived and prompt decays. This search looks for pair production of the scalar mediators at the LHC, yielding events with two SM jets and two emerging jets.

As the detector signature left by such dark sector showers significantly deviates from the assumptions made when designing the detector, a fully data-based method is used for evaluating the number of standard model events that can be mistaken as signal events. The search is carried out on data collected by the CMS experiment corresponding to an integrated luminosity of 138 /fb , and we observe no significant excess. The results are interpreted using two dark sector models and exclude mediator masses up to 1750 GeV for an unflavored dark QCD model and up to 2000 GeV for a flavored-aligned dark QCD model.