Karol Krizka (U. Chicago) "Dark Matter Mediators and Dijet Resonance Searches by the ATLAS Experiment"

Abstract:
Using 13 TeV pp collisions, the ATLAS experiment has used a collection of dijet resonance searches (high-mass dijet, trigger-level dijet and dijet+ISR) to search for new particles with masses ranging from 200 GeV to 7 TeV. This talk summarizes the searches, with a focus on new the “dijet+ISR” channel. The dijet+ISR analysis is an LHC-first and reaches mediator masses below 500 GeV by utilizing an ISR jet or photon to trigger the event. This region was previously accessible only by the LEP and Tevatron experiments. This is an important improvement for Dark Matter simplified models, based on a mediator between a Dark Matter particle and the Standard Model. Cosmological measurements of the Dark Matter relic density prefer the mediator mass to be sub-TeV. By searching for a dijet resonance produced by the mediator decaying back into quarks, powerful new limits are set on the simplified Dark Matter models.