Study of the Z Boson Production at the ATLAS Experiment with First Data

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.