The Art of Finding Needles in Haystacks: Event Selection at ATLAS

Adriana Milic examines how the ATLAS liquid-argon calorimeter supports rapid event selection. After introducing its readout architecture, she explains the Phase-I change from analogue triggering to finely segmented digital Super Cells. Increased granularity, precision and dynamic range enable better background rejection during high-pile-up Run 3 collisions. Finer segmentation also changes signal-to-noise behaviour and the efficiency for low-energy deposits, creating distinct challenges in heavy-ion data taking. The seminar then considers Phase-II plans for greater bandwidth and full-calorimeter information, enabling more sophisticated selection under the conditions expected at the High-Luminosity LHC.