Clusters of topologically connected calorimeter cells around cells with large absolute signal-to-noise ratio (topo-clusters) are the basis for calorimeter signal reconstruction in the ATLAS experiment. Topological cell clustering has proven performant in LHC Runs 1 and 2. It is, however, susceptible to out-of-time pile-up of signals from soft collisions outside the 25 ns proton-bunch-crossing window associated with the event’s hard collision. To reduce this effect, a calorimeter-cell timing criterion was added to the signal-to-noise ratio requirement in the clustering algorithm. Multiple versions of this criterion were tested by reconstructing hadronic signals in simulated events and Run 2 ATLAS data. The preferred version is found to reduce the out-of-time pile-up jet multiplicity by ∼50% for jet pT∼20 GeV and by ∼80% for jet pT≳50 GeV, while not disrupting the reconstruction of hadronic signals of interest, and improving the jet energy resolution by up to 5% for 20<30 GeV. Pile-up is also suppressed for other physics objects based on topo-clusters (electrons, photons, τ-leptons), reducing the overall event size on disk by about 6% in early Run 3 pile-up conditions. Offline reconstruction for Run 3 includes the timing requirement.

Zwalinski, L., Zou, W., Zormpa, O., Zorbas, T.G., Zoch, K., Zoccoli, A., et al. (2024). Improving topological cluster reconstruction using calorimeter cell timing in ATLAS. THE EUROPEAN PHYSICAL JOURNAL. C, PARTICLES AND FIELDS, 84(5) [10.1140/epjc/s10052-024-12657-1].

Improving topological cluster reconstruction using calorimeter cell timing in ATLAS

Cerri A.;
2024-01-01

Abstract

Clusters of topologically connected calorimeter cells around cells with large absolute signal-to-noise ratio (topo-clusters) are the basis for calorimeter signal reconstruction in the ATLAS experiment. Topological cell clustering has proven performant in LHC Runs 1 and 2. It is, however, susceptible to out-of-time pile-up of signals from soft collisions outside the 25 ns proton-bunch-crossing window associated with the event’s hard collision. To reduce this effect, a calorimeter-cell timing criterion was added to the signal-to-noise ratio requirement in the clustering algorithm. Multiple versions of this criterion were tested by reconstructing hadronic signals in simulated events and Run 2 ATLAS data. The preferred version is found to reduce the out-of-time pile-up jet multiplicity by ∼50% for jet pT∼20 GeV and by ∼80% for jet pT≳50 GeV, while not disrupting the reconstruction of hadronic signals of interest, and improving the jet energy resolution by up to 5% for 20<30 GeV. Pile-up is also suppressed for other physics objects based on topo-clusters (electrons, photons, τ-leptons), reducing the overall event size on disk by about 6% in early Run 3 pile-up conditions. Offline reconstruction for Run 3 includes the timing requirement.
2024
Zwalinski, L., Zou, W., Zormpa, O., Zorbas, T.G., Zoch, K., Zoccoli, A., et al. (2024). Improving topological cluster reconstruction using calorimeter cell timing in ATLAS. THE EUROPEAN PHYSICAL JOURNAL. C, PARTICLES AND FIELDS, 84(5) [10.1140/epjc/s10052-024-12657-1].
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11365/1317578