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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 p T ∼ 20 GeV and by ∼ 80 % for jet p T ≳ 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, 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. [ABSTRACT FROM AUTHOR]

Measurements of the differential production cross-sections of prompt and non-prompt J / ψ and ψ (2 S) mesons with transverse momenta between 8 and 360 GeV and rapidity in the range | y | < 2 are reported. Furthermore, measurements of the non-prompt fractions of J / ψ and ψ (2 S) , and the prompt and non-prompt ψ (2 S) -to- J / ψ production ratios, are presented. The analysis is performed using 140 fb - 1 of s = 13 TeV pp collision data recorded by the ATLAS detector at the LHC during the years 2015–2018. [ABSTRACT FROM AUTHOR]