The ATLAS LAr Calorimeter Level 1 Trigger Signal pre-Processing System: Installation, Commissioning and Calibration Results.

The Liquid Argon calorimeter is one of the main sub-detectors in the ATLAS experiment at the LHC. It provides precision measurements of electrons, photons, jets and missing transverse energy produced in the LHC pp collisions. The calorimeter information is a key ingredient in the first level (L1) trigger decision to reduce the 40 MHz p-p bunch crossing rate to few 100 kHz of accepted events waiting to be readout in full precision, in the system pipelines. This presentation covers the LAr calorimeter electronics used to prepare signals for the L1 trigger. After exiting the cryostat, part of the current signal, at the front end, is directly split off the main readout path and summed with neighbouring channels forming trigger towers which are transmitted in analog form over 50 to 70 meters to the counting room. There, the signals are calibrated, reordered and futher summed for fast digitization using the L1 trigger hardware. Many factors like calorimeter capacitances and pulse shapes have to be taken into account in this process, which collects about 180000 channels into some 3500 analog signals through a sophisticated system of boards, special cables, crates with its own control and monitoring system. The system has been fully installed and is currently used for taking the commissioning data necessary to calibrate the L1 signals and estimate and correct with calibration signals the scaling and timing differences for different ele ctromagnetic layers. Analysis tools have been developed to study the pulse shape, time and amplitude for both the precision readout and the L1 signals. We show performance studies using real data from cosmic and/or first beam data.