Dilepton final states with ATLAS at √s = 7 TeV

This thesis proposes a method to measure the simultaneous production of a high momentum electrons and muons in proton proton collisions at the Large Hadron Collider (LHC) at a centre of mass energy of 7 TeV. The method is implemented for data collected by the ATLAS detector, and measures electron-muon final state events as a function of observed missing transverse momentum vs. number of jets. The three major processes, Z → τ+ τ-, top anti-top and W+W- are fitted simultaneously using a maximum likelihood fit. This method is shown to be an interesting alternative to the widely used exclusive fit method. Through test of fit against both pseudo data and some of the most recently recorded data at the LHC, the method proves to give better statistical uncertainties than any currently published by ATLAS for the top-antitop cross section and could yield interesting cross section measurements of Z → τ+ τ- and W+W-. Furthermore the method is shown to be an interesting probe for new physics and a 10 jet event is presented graphically as an example of this.