Model independent sparticle mass measurements at ATLAS

This thesis presents a method by which masses of supersymmetric particles might be deduced from end points of kinematic distributions obtained by the ATLAS experiment. An assumption at the core of the analysis is the existence of the mass hierarchy: mass of neutralino one < mass of right slepton < mass of neutralino two < mass of squark. Care is taken to keep the number of additional model-dependent assumptions as small as possible, so that the otherwise model-independent nature of the method may be emphasized. Strengths and weaknesses of the method, as well as its degree of model independence, are investigated by applying it to events simulated in accordance with two different supersymmetric models, and corresponding to an integrated luminosity of 100 inverse fb. The method is shown to be largely successful in both models; principally constraining mass differences, but also allowing absolute masses to be determined with a statistical and energy scale error of 20 to 30 GeV in the models considered. It is observed that special care should be taken when interpreting results concerning the slepton masses. Under some circumstances the model independence of the method can result in the light slepton mass failing to be uniquely determined. However, it is also demonstrated that, when this problem does not arise, it can even be possible to obtain a ``bonus'' measurement of the mass of a heavier slepton such as the left slepton.