PT Journal AU ATLAS Collaboration (Aad, Gea Aikot, A Amos, KR Aparisi Pozo, JA Bailey, AJ Bouchhar, N Cabrera Urban, S Cantero, J Cardillo, F Castillo Gimenez, V Chitishvili, M Costa, MJ Didenko, M Escobar, C Fiorini, L Fullana Torregrosa, E Fuster, J Garcia, C Garcia Navarro, JE Gomez Delegido, AJ Gonzalez de la Hoz, S Gonzalvo Rodriguez, GR Guerrero Rojas, JGR Lacasta, C Marti-Garcia, S Martinez Agullo, P Miralles Lopez, M Mitsou, VA Monsonis Romero, L Moreno Llacer, M Munoz Perez, D Navarro-Gonzalez, J Poveda, J Prades IbaƱez, A Rubio Jimenez, A Ruiz-Martinez, A Sabatini, P Saibel, A Salt, J Sanchez Sebastian, V Sayago Galvan, I Senthilkumar, V Soldevila, U Sanchez, J Torro Pastor, E Valero, A Valiente Moreno, E Valls Ferrer, JA Varriale, L Villaplana Perez, M Vos, M TI Improving topological cluster reconstruction using calorimeter cell timing in ATLAS SO European Physical Journal C JI Eur. Phys. J. C PY 2024 BP 455 - 42pp VL 84 IS 5 DI 10.1140/epjc/s10052-024-12657-1 LA English AB 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 similar to 50% for jet p(T) similar to 20 GeV and by similar to 80% for jet p(T) greater than or similar to 50 GeV, while not disrupting the reconstruction of hadronic signals of interest, and improving the jet energy resolution by up to 5% for 20 < p(T) < 30 GeV. Pile-up is also suppressed for other physics objects based on topo-clusters (electrons, photons, tau -leptons), reducing the overall event size on disk by about 6% in early Run 3 pileup conditions. Offline reconstruction for Run 3 includes the timing requirement. ER