Pulse shapes for signal reconstruction in the ATLAS Tile Calorimeter

The Tile Calorimeter for the ATLAS experiment at the CERN Large Hadron Collider (LHC) is ready for data taking with the proton-proton collisions. The Tile Calorimeter is a sampling calorimeter with iron absorber and scintillators as active medium. The scintillators are read out by wavelength shifting fibers and photomultiplier tubes. The analogue signals from the PMTs are digitized by sampling the PMT signals every 25 ns. For each interesting event selected by the ATLAS trigger, the Tile Calorimeter reads out seven consecutive samples, thus covering a time window of 175 ns. The seven consecutive samples are combined by the electronics in a remote counting room, at a rate of up to 100 kHz, to compute the pulse amplitudes and their position in time. These quantities are required for energy reconstruction. A solid understanding of the pulse shapes in the calorimeter is required for an accurate energy reconstruction. Systematic studies of the pulse shapes in the ATLAS Tile Calorimeter have been performed by exposing modules of the calorimeter to single pions in test beam runs. These studies are presented and the implications for energy reconstruction are given.