Public Heavy Ion Trigger Plots for Collision Data

Introduction

Approved plots that can be shown by ATLAS speakers at conferences and similar events. Please do not add figures on your own. Contact the responsible project leader in case of questions and/or suggestions.

2017 XeXe Data

Performance of Level-1 total energy triggers for low-pT diphoton events ATL-COM-DAQ-2018-036 (May 27, 2018)

Distribution of total transverse energy (TE) at Level-1 in minimum-bias events (black circles) and exclusive e+e- event candidates (blue squares) in Xe+Xe data. The minimum-bias events are selected using a logical OR of two triggers, first one requiring Level-1 TE less than 4 GeV and at least one track at HLT and a second one requiring Level-1 TE greater than 4 GeV. The offline event selection is made for the purpose of Level-1 TE trigger efficiency measurement. The exclusive e+e- pairs have a very similar signature to diphoton events that we are interested in, but they have larger production cross-section. The exclusive e+e- event candidates are selected offline by a set of requirements: exactly two oppositely-charged tracks with pT > 1 GeV matched to electromagnetic clusters with ΔR < 0.7 and accompanied by the minor detector activity described by the sum of pT of remaining tracks to be less than 2 GeV. Two tracks are required to be in a back-to-back configuration in the azimuthal angle (acoplanarity < 0.2). The shaded area around the points represents statistical uncertainties.	png pdf eps
Efficiency of total transverse energy (TE) triggers at Level-1: TE4 (full circles) and TE5 (open squares), with optimised Level-1 calorimeter noise settings as a function of the sum of transverse energy of two electromagnetic clusters satisfying the exclusive e+e- event selection in Xe+Xe data. Triggers have 4 GeV and 5 GeV thresholds on TE at Level-1, respectively. The fit represents a Level-1 TE5 trigger efficiency measured in 2015 Pb+Pb data using non-optimised Level-1 calorimeter noise settings. The comparison proves higher trigger efficiency after optimization. The trigger efficiency is measured in minimum-bias events selected by a logical OR of two triggers, first one requiring Level-1 TE less than 4 GeV and at least one track at HLT and a second one requiring Level-1 TE greater than 4 GeV. The exclusive e+e- event candidates are selected offline by a set of requirements: exactly two oppositely-charged tracks with pT > 1 GeV matched to electromagnetic clusters with ΔR < 0.7 and accompanied by the minor detector activity described by the sum of p_T of remaining tracks to be less than 2 GeV. Two tracks are required to be in a back-to-back configuration in the azimuthal angle (acoplanarity < 0.2).	png pdf eps
Correlation between transverse energy of two offline electromagnetic clusters matched to offline tracks satisfying the exclusive e+e- candidate requirements in Xe+Xe data. The exclusive e+e- event candidates are selected offline by a set of requirements: exactly two oppositely-charged tracks with pT > 1 GeV matched to electromagnetic clusters with ΔR < 0.7 and accompanied by the minor detector activity described by the sum of pT of remaining tracks to be less than 2 GeV. Two tracks are required to be in a back-to-back configuration in the azimuthal angle (acoplanarity < 0.2).	png pdf eps
Acoplanarity distribution of two tracks from the exclusive e+e- event candidates in Xe+Xe data. The exclusive e+e- event candidates are selected offline by a set of requirements: exactly two oppositely charged tracks with pT > 1 GeV matched to electromagnetic clusters with ΔR < 0.7 and accompanied by the minor detector activity described by the sum of pT of remaining tracks to be less than 2 GeV. Two tracks are required to be in a back-to-back configuration in the azimuthal angle (acoplanarity < 0.2).	png pdf eps