Signal Processing for the ATLAS Liquid Argon Calorimeter : studies and implementation

The ATLAS detector operated successfully in the LHC studying the pp collisions produced with an energy up to 8 TeV in the center of mass. During the period from 2009 to 2012, called the LHC Run 1, up to more than 36 independent collisions were produced every 50 ns at the LHC. The ATLAS detector has a set of calorimeters measuring the energy of different types of particles. The liquid argon calorimeters work by ionization of their active material and the free electrons are collected by electrodes at high voltages. The generated current signal has a well known pulse shape. Multiple samples of the analog signal are collected and digital signal processing techniques are used to extract its amplitude which is related to the energy deposited. The signal pulse is relatively long (up to 400 ns) and the probability of background events happening in the same detector area during that interval is high. A technique called optimal filtering is used to minimize the effects of such pile-up. In the next data taking period, the luminosity will be higher and new techniques are being considered to mitigate the impact of the pile-up induced noise. Such techniques are also being envisaged for usage in the ATLAS trigger. This paper will discuss these techniques and their implementation in the new ATCA standard. A prototype using the processing power of FPGAs is being prepared for studies and may be used when the LHC returns to operation in 2015.