Higgs boson searches within ATLAS: combination of channel sensitivities and extension of search range to heavy masses

A comparison of the two statistical frameworks, MCLimits and RooStats is presented in relation to the statistical combination of the decay channels of the Standard Model Higgs boson using data collected by the ATLAS experiment in the period up to the end of the 2012 LHC run. A wrapper mechanism designed to allow the RooStats model and data containers to be compatible with MCLimits is described. This interface is used to produce statistical plots for single channel and full combination Higgs searches. The MCLimits and RooStats results are compared and contrasted, showing good agreement throughout the mass range, acting as a double check of the published results. The extension of the Higgs mass search range above 600 GeV is discussed, including a summary of the Complex Pole Scheme. The implementation of the Complex Pole Scheme is necessary in analyses considering a heavier Higgs-like particle. A framework was created to adjust existing Monte Carlo samples to give an approximation of the Complex Pole Scheme. This allowed quick implementation of this theory and studies of the effects on the existing analyses without the large scale tasks of rerunning all relevant Monte Carlo samples. The framework was adapted to be as general as possible to allow for the inclusion and study of other theories and modifications.