Timing behavior of the ATLAS Pixel Detector in calibration, cosmic-ray and collision data

The ATLAS Pixel Detector is the innermost tracking detector of the ATLAS experiment at the Large Hadron Collider (LHC) at CERN. It consists of 1744 identical modules built using a hybrid silicon pixel detector technology with in total 80 million readout channels. As with all LHC detectors the Pixel detector is designed to distinguish signal hits from two subsequent bunch crossings with the time interval of 25 ns (or 1 BC) at the full LHC luminosity. Due to the timewalk effect in the front-end electronics and propagation delays in the readout circuitry each detector module requires individual timing adjustment with a precision of about 1 ns. Such precision, which is far below detector intrinsic timing resolution of 25 ns, has been achieved by taking collision data with known timing offsets and analyzing timing distribution of hits from particle tracks. In the paper the measured timing characteristics of the modules are analyzed and the timing optimization process is described.