Simultaneous measurement of the top quark pair production cross-section and the Rb in the atlas experiment

This thesis describes the simultaneous measurement of the top pair production cross-section together with the Rb parameter in the lepton plus jets channel with 1 inverse fb of the 2011 data at 7 TeV obtained with the ATLAS experiment at the LHC. Events are categorized in 18 orthogonal channels, depending on the lepton flavor (electrons or muons), the jet multiplicity (3, 4, or 5 jets) and the b-tagging multiplicity (0, 1, or 2 tags). With 1 inverse fb of luminosity, the ttbar cross-section measurement is limited by systematic uncertainties and much effort has been put into trying to quantify and, when possible, limit their impact on the overall measurement precision. The analysis also includes a measurement of Rb , which has not been performed in ATLAS yet. The Rb parameter is related to the |VtX| mixing matrix elements and, in combination with the single top cross section measurement, can be used to set quasi model independent constraints on their magnitudes. In addition, it is sensitive to new physics with heavy-flavour content larger than the one predicted by the SM processes.