Pursuit of paired dijet resonances in the Run 2 dataset with ATLAS

New particles with large masses that decay into hadronically interacting particles are predicted by many models of physics beyond the Standard Model. A search for a massive resonance that decays into pairs of dijet resonances is performed using..

Search for a new pseudoscalar decaying into a pair of muons in events with a top-quark pair at s=13 TeV with the ATLAS detector

A search for a new pseudoscalar Formula Presented-boson produced in events with a top-quark pair, where the Formula Presented-boson decays into a pair of muons, is performed using Formula Presented Formula Presented collision data collected with the ATLAS detector at the LHC, corresponding to an integrated luminosity of Formula Presented. The search targets the final state where only one top quark decays to an electron or muon, resulting in a signature with three leptons Formula Presented and Formula Presented. No significant excess of events above the Standard Model expectation is observed and upper limits are set on two signal models: Formula Presented and Formula Presented with Formula Presented, Formula Presented, where Formula Presented, in the mass ranges Formula Presented and Formula Presented

Fast b-tagging at the high-level trigger of the ATLAS experiment in LHC Run 3

The ATLAS experiment relies on real-time hadronic jet reconstruction and b-tagging to record fully hadronic events containing b-jets. These algorithms require track reconstruction, which is computationally expensive and could overwhelm the high-level-trigger farm, even at the reduced event rate that passes the ATLAS first stage hardware-based trigger. In LHC Run 3, ATLAS has mitigated these computational demands by introducing a fast neural-network-based b-tagger, which acts as a low-precision filter using input from hadronic jets and tracks. It runs after a hardware trigger and before the remaining high-level-trigger reconstruction. This design relies on the negligible cost of neural-network inference as compared to track reconstruction, and the cost reduction from limiting tracking to specific regions of the detector. In the case of Standard Model HH → bb̅bb̅, a key signature relying on b-jet triggers, the filter lowers the input rate to the remaining high-level trigger by a factor of five at the small cost of reducing the overall signal efficiency by roughly 2%