Identification of Pile-up Using the Quality Factor of Pulse Shapes in the ATLAS Tile Calorimeter

The ATLAS experiment records data from the proton-proton collisions produced by the Large Hadron Collider (LHC). The Tile Calorimeter is the hadronic sampling calorimeter of ATLAS in the region |η|<1.7. It uses iron absorbers and scintillators as active material. The LHC will provide collisions every 25 ns, putting very strong requirements on the energy measurement in presence of energy deposits from different collisions in the same read out window and physical calorimeter channel (pile-up). In 2011 the LHC was running with filled bunches at 50 ns spacing and at intensities which yield up to about 8 proton-proton collisions per bunch crossing. We present a quality factor that is computed offline for each collision and for each calorimeter channel, and provide criteria to detect pile-up in TileCal channels. The quality factor can be used to select channels that need a special treatment to account for large energy deposition from pile-up.Technical report from the ATLAS experiment.