Particle Identification Using the Time-over-threshold Method in the ATLAS Transition Radiation Tracker

The Transition Radiation Tracker (TRT) in the ATLAS Inner Detector was designed to be a powerful tracking device and to provide electron identification via transition-radiation detection. The TRT is a straw drift-tube detector, with a central barrel section and two end-cap sides, which will give an average of 35 straws crossed per track. Part of the barrel TRT is presently in construction at Indiana University. The straw tubes are filled with a Xe-based gas mixture, that strongly absorbs transition-radiation photons produced by the passage of ultra-relativistic charged particles (electrons) in the radiator material which surrounds the straws. The straw output signal is discriminated in the front-end electronics at a low-threshold level (200 eV) and at a high-threshold level (5000 eV). This thesis describes a novel technique for particle identification with the ATLAS TRT. Detailed Monte Carlo simulation and test-beam experiments lead to the the conclusion that time-over-threshold measurements can improve electron identification at low energy. Time-over-threshold is defined as the width of the discriminated signal above the low-threshold level. The use of time-over-threshold also provides some kaon-pion separation, thereby significantly enhancing the B-physics capabilities of the ATLAS detector. The application of this novel technique for the study of the decay B → KKπ is described in this thesis.