The performance of the jet trigger for the ATLAS detector during 2011 data taking

Area of Science:

• High Energy Physics
• Particle Detection
• Collider Physics

Background:

• The Large Hadron Collider (LHC) operates at high collision rates (40 MHz).
• The ATLAS detector requires a sophisticated trigger system to select interesting events for storage.
• Jet triggers are essential for identifying and analyzing particle jets produced in collisions.

Purpose of the Study:

• To evaluate the performance of the ATLAS jet trigger system during the 2011 LHC data-taking period.
• To determine the efficiency and resolution of jet reconstruction at different trigger levels.
• To assess the trigger's capability in selecting jets from proton-proton and heavy-ion collisions.

Main Methods:

• Analysis of data collected during the 2011 LHC run (7 TeV pp, 2.76 TeV/nucleon heavy ions).
• Evaluation of a three-level trigger system designed to reduce event rates from 40 MHz to 400 Hz.
• Characterization of jet transverse energy thresholds and trigger efficiency curves.

Main Results:

• The jet trigger achieved full efficiency for jets with transverse energy > 25 GeV (Level 1 random seeding).
• Full efficiency for jets identified across all three trigger levels was reached for offline jets > 60 GeV.
• Reconstructed jets (> 60 GeV) showed excellent transverse energy resolution (< 4% central, < 2.5% forward).

Conclusions:

• The ATLAS jet trigger system demonstrated high performance and efficiency in 2011.
• The trigger effectively selects high-transverse-energy jets, enabling detailed physics analyses.
• The achieved resolution is vital for precise measurements of jet properties at the LHC.