Search for Low-Mass Dijet Resonances Using Trigger-Level Jets at the ATLAS Detector

Conventional dijet resonance searches at the Large Hadron Collider are statistically limited for sub-TeV resonance masses by the bandwidth of the data acquisition systems. The presented search explores this mass range at unprecedented statistical precision by utilizing a partial event readout consisting of jets reconstructed by the ATLAS High-Level Trigger using only calorimeter information. Proton-proton collisions at a centre-of-mass energy of $\sqrt{s}$ = 13 TeV corresponding to an integrated luminosity of up to 132 fb$^{-1}$ are analyzed. A dedicated calibration for the trigger-level jets is applied and two complementary, data-driven background estimates with very high statistical precision are presented. No significant excess over the background expectation is observed and exclusion limits on dijet resonance cross sections are derived. These represent the most stringent constraints on narrow, Gaussian-shaped dijet resonances in the mass range of 375–1200 GeV in general and in the range of 375–1500 GeV for an axial-vector Dark Matter mediator coupling to quarks in particular.