Evaluation of the Timing Performance of the ATLAS LAr Calorimeter Digital Trigger (DT)

The ATLAS Liquid Argon calorimeter provides energies to the first level calorimeter trigger at 40 MHz with high granularity, relying on a good timing performance to correctly identify the bunch crossing from which the energy deposits originate. Using a calibration dataset, I quantify the intrinsic timing of electromagnetic super-cells, compare three reference-time definitions
derived from the main readout cell times, and study the resolution. The energy-weighted cell average yields the sharpest ∆t = tSC −tref core across layers and thresholds. In the electromagnetic barrel Layer 2 the intrinsic resolution improves from about 4.7 ns at 1 GeV to 2 GeV to roughly 0.7 ns above 20 GeV. Residual biases remain within ±0.5 ns. The results show subnanosecond timing resolution for the super cells at moderate energies and provide a baseline for additional digital trigger and trigger timing studies.