ATLAS Level-1 Calorimeter Trigger: Timing Calibration with 2009 LHC Beam Splashes

The ATLAS Level-1 Calorimeter Trigger (L1Calo) identifies high-pT objects and measures the total and missing ET in the Tile and Liquid Argon Calorimeters. L1Calo is a hardware based, pipelined system built with custom electronics. Starting with 7200 pre-summed analogue signals received from the calorimeters, the Preprocessor Module conditions and digitizes these signals at the LHC bunch-crossing frequency of 40 MHz. Sampling the peak of the signal is important for assigning the bunch-crossing identification and calculating the deposited energy. A nanosecond-step time offset is applied independently to each channel to optimize this sampling. This offset was calibrated using beam splash events provided by the LHC in November 2009. The obtained timing results and procedure are presented here.