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

by Adriana Milic (CERN)

Thursday 5 Nov 2026, 10:00 → 12:00 Europe/Berlin

Käthe-Kümmel-Str. 1/U1.059 (ROT) - Conference Room (ROT)

Abstract: 

 

The ATLAS Liquid Argon calorimeter plays a central role in the experiment’s trigger system, providing fast measurements of electromagnetic and hadronic energy deposits for the Level-1 trigger. This seminar will first give a brief introduction to the LAr calorimeter and its readout architecture, before focusing on the trigger system and its recent evolution.

Particular emphasis will be placed on the Phase-I trigger upgrade, which replaced the previous analogue trigger readout with a fully digital system based on finely segmented Super Cells. The upgrade increased the granularity of the information available to the Level-1 trigger by up to a factor of ten, while also improving the precision and dynamic range of the measurements. This additional information enables more sophisticated trigger algorithms and significantly improves the rejection of backgrounds, helping ATLAS maintain efficient triggers in the high-pile-up environment of Run 3.

The seminar will then discuss some of the less obvious consequences of the new trigger architecture. In particular, the finer segmentation changes the signal-to-noise conditions at trigger level and can affect the efficiency for low-energy interactions. This is especially relevant for heavy-ion physics, where interesting processes can produce relatively low-energy deposits and where the trigger requirements differ substantially from those of high-pile-up proton-proton collisions. Recent experience with the digital trigger will be used to illustrate these effects and the challenges they pose for heavy-ion data taking.

Finally, the seminar will look towards the Phase-II upgrade, which will provide even higher bandwidth and the full calorimeter information to the upgraded trigger system. I will enable an even more sophisticated event selection in the challenging high-pile-up environment expected at the HL-LHC.

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https://uni-bonn.zoom-x.de/j/66253567797?pwd=R2MrNmNCQnl4K1hSejd6VnBEYXJ2QT09

Meeting ID: 662 5356 7797
Passcode: 599591