Constraining the supersymmetric parameter space with early data from the Compact Muon Solenoid experiment.

The year 2010 saw the Large Hadron Collider (LHC) collect 35.1 pb−1 of 7 TeV proton-proton collision data. This thesis reports on the work carried out by the candidate as part of the calculation of the first constraints placed upon the supersymmetric parameter space using measurements made with this data. In particular, the development and application of the kinematic techniques used to ensure that the search was robust to detector mismeasurements, inherent in any early phase of data-taking, are discussed. The Constrained Minimally Supersymmetric Standard Model (CMSSM) model is introduced to demonstrate how a supersymmetric model may extend the Standard Model of particle physics, and is used as the benchmark signal to examine how supersymmetry may manifest in 7 TeV proton-proton collisions. The role of kinematics in early searches for such signals is then discussed; given the final state topology of interest (particle jets and large missing transverse momentum), it is useful to explore how the event kinematics can be exploited to mitigate for errors that are due to detector mismeasurements. A search strategy based upon these principles and applied to the full Compact Muon Solenoid (CMS) experiment is then described, as used in the first published search for supersymmetry with LHC data reported in Phys. Lett. B 698 (2011) 196. The importance of robustness to mismeasurement is emphasised, and the kinematic characterisation of events is exploited to ensure that the search is indeed robust. The thesis concludes with a summary of the search results. The observed number of events fulfilling the signal criteria is compatible with that expected from the Standard Model alone. The subsequent exclusion limits, given at the 95% Confidence Limit, place significantly greater constraints upon the supersymmetric parameter space than those of previous experiments.