A new method for mapping detector material in situ and a matrix element approach to the search for heavy di-muon resonances at the LHC

The Standard Model of particle physics has proven to be a very successful theory to describe the fundamental interactions and elementary particles observed in nature. The discovery of a Higgs boson in 2012 by the Atlas and CMS experiments at the LHC has been the ultimate confirmation of the predictions of the theory. However, this model does not have answers to everything at the fundamental level. For example, the inclusion of the gravitational force and the hierarchy problem are among the questions awaiting to be answered. Moreover, it is believed that the fundamental forces could be unified into a single force. Many new theoretical models that address these problems predict the existence of new heavy particles at the TeV scale and even new extra space dimensions. An experimentally and particularly appealing final state to search for these new phenomena at the LHC collider is the di-muon final state. However, no evidence for such new particles has been found so far, indicating that these particles might be heavier and produced at a lower rate than expected. By improving the reconstruction and analysis techniques, the sensitivity of these searches can be enhanced. This thesis presents the results of research performed along both of these lines. First, a new method for mapping the distribution of detector material has been developed and applied to the inner tracker detector of the CMS experiment. The method exploits the scattering of charged particles off the nuclei of the material of a high-energy physics experiment to infer the distribution of the material itself. The method is easily applicable and its accuracy is comparable to that of more traditional methods. The method also proves to be complementary to such traditional methods in that it suffers from different sources of uncertainty. Second, a matrix element based analysis approach has been developed and tested to improve the sensitivity for a discovery of a di-muon resonance. It is found that the analysis method is robust, reliable and advantageous to use in the searches at the LHC.(SC - Sciences) -- UCL, 2015Accès libre25/09/2015(SC - Sciences) -- UCL, 2015Anglai