Measurement of the top-quark pair production cross section with soft muon b-tagging in pp collisions at [Square root] s = 7 TeV with the Atlas detector

This thesis presents a study of the measurement of the top pair production cross section in the semileptonic decay channel with soft muon b-tagging at the Atlas detector using early LHC data. A theoretical overview of current research in particle physics, motivating the construction of the LHC and the Atlas detector is discussed followed by the main motivations behind a measurement of the top cross section. A summary of my work undertaken for the semiconductor tracker (SCT) collaboration on Atlas, including shift work and the refurbishment of the SR1 barrel sector and spare endcap disk is detailed. Following this the electron isolation in top and Z boson events was examined with Monte Carlo simulated events to optimise the selection criteria for electrons from W boson decay in top events. As part of the top cross section measurement, the e ciency and scale factor, compared to Monte Carlo studies, of using a 2 match cut on soft muons was calculated using the decay of the J= in early LHC data. The last chapter details the development of an analysis framework and measurement of the top pair production in the semileptonic decay channel with soft muon b-tagging. This measurement builds on the work in the previous chapters utilising both the electron isolation requirement from Monte Carlo simulations and the scale factor on the soft muon 2 match cut for b-tagging to yield a measurement of the top cross section in 2.9 pb􀀀1 of LHC data.