Electron track reconstruction in the ATLAS experiment

Before entering the hardware production phase of a HEP experiment, the detector elements that have been chosen during the planning process need to be thoroughly tested. At the LHC, silicon detectors will operate in a high-rate environment which requires low-noise electronics with a shaping time of $25 s$. A prototype silicon-strip half-module equipped with the analogue read-out chip SCTA128-HC was put in a $200GeV$ pion beam. An analysis of the collected data is presented. The tested module was found to conform to the SCT-modules specification for the ATLAS experiment. Electron reconstruction in the ATLAS detector is compromised by the large amount of material in the tracking volume, which leads to frequent emissions of hard bremsstrahlung photons. This affects the measurement of the transverse projections of track parameters in the inner detector as well as the measurement of energy and azimuthal angle in the EM calorimeter for $p_T<20GeV$. Reconstruction and electron identification efficiencies are both degraded. A detailed analysis of bremsstrahlung effects has been performed and it is shown that a first-order treatment is unsatisfactory. An algorithm for efficient and robust electron reconstruction has been developed which placed a strong emphasis on bremsstrahlung detection and recuperation so as to provide the best possible track parameters from the ID reconstruction. The algorithm was benchmarked against simulated data: single electrons, electrons in jets and electrons in the presence of high-luminosity pile-up. The $Bo o protectJpsi o ee$ and $Z o ee$ processes, crucial for EM calorimeter calibration, as well as the potential Higgs discovery via $H o ZZ^{(star)} o 4e$ (for $m_{H}$=130, 150, 180, $200GeV$), were studied using the developed electron reconstruction algorithm. Typically, a 10% improvement of reconstruction efficiency has been achieved for these channels with respect to the results quoted in the ATLAS emph{Physics Performance TDR}. At low and intermediate electron $p_T$ values, the experimental parameter resolution has likewise been improved with a better understanding and handling of the bremsstrahlung effects.