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Schott, Matthias (2007): Study of the Z Boson Production at the ATLAS Experiment with First Data. Dissertation, LMU München: Fakultät für Physik



The ATLAS detector, currently in its final installation phase at CERN, is designed to provide precise measurements of 14 TeV proton-proton collisions at the Large Hadron Collider. The measurements of the cross section and transverse momentum spectrum of the Z boson production at LHC provides first tests of the standard model in a new energy domain and may reveal exotic physics processes. Moreover, the properties of the Z boson resonance and its decay into two muons are known to very high precision from LEP experiments and hence can be used as a physics process for calibration and alignment. The Z boson production is also a common background process for many other physics analyses and must therefore be well understood. This thesis describes a measurement strategy of the cross section s for the process pp->Z->(mu)(mu) at the ATLAS experiment during its startup phase. As a result of this study a precision of d(sigma)/ (sigma) = 0.006(stat) + 0.008(sys) + 0.01 (pdf) is expected for an integrated luminosity of 50 pb^(-1), assuming a fully operational ATLAS detector, not including uncertainties in the luminosity measurements. A major goal of the approach presented was to minimize the dependence on Monte Carlo simulations. Hence, several methods for the determination of the detector response based on data have been studied. In addition, a strategy for the differential cross section measurement of the transverse momentum of the Z boson has been developed. In contrast to a measurement of the total cross section, it is expected that the statistical uncertainty dominates for the given integrated luminosity of 50 pb^(-1). The predicted high pT resolution of the ATLAS Inner Detector and the Muon Spectrometer allow for the first observation of interesting parton distribution effects, i.e. the so-called x-broadening, even with the limited statistics expected during the first data taking period.