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 $${\sim }50\%$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mo>∼</mml:mo> <mml:mn>50</mml:mn> <mml:mo>%</mml:mo> </mml:mrow> </mml:math> for jet $$p_{\textrm{T}}\sim 20$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:msub> <mml:mi>p</mml:mi> <mml:mtext>T</mml:mtext> </mml:msub> <mml:mo>∼</mml:mo> <mml:mn>20</mml:mn> </mml:mrow> </mml:math> GeV and by $${\sim }80\%$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mo>∼</mml:mo> <mml:mn>80</mml:mn> <mml:mo>%</mml:mo> </mml:mrow> </mml:math> for jet $$p_{\textrm{T}} \gtrsim 50$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:msub> <mml:mi>p</mml:mi> <mml:mtext>T</mml:mtext> </mml:msub> <mml:mo>≳</mml:mo> <mml:mn>50</mml:mn> </mml:mrow> </mml:math> GeV, while not disrupting the reconstruction of hadronic signals of interest, and improving the jet energy resolution by up to 5% for $$20< p_{\textrm{T}} < 30$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mn>20</mml:mn> <mml:mo><</mml:mo> <mml:msub> <mml:mi>p</mml:mi> <mml:mtext>T</mml:mtext> </mml:msub> <mml:mo><</mml:mo> <mml:mn>30</mml:mn> </mml:mrow> </mml:math> GeV. Pile-up is also suppressed for other physics objects based on topo-clusters (electrons, photons, $$\tau $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mi>τ</mml:mi> </mml:math> -leptons), reducing the overall event size on disk by about $$6\%$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mn>6</mml:mn> <mml:mo>%</mml:mo> </mml:mrow> </mml:math> in early Run 3 pile-up conditions. Offline reconstruction for Run 3 includes the timing requirement.
Tópico:
Particle physics theoretical and experimental studies
