Data-driven determination of Z(vv) background to new-physics searches with jets and missing transverse momentum at CMS

The CMS experiment at the Large Hadron Collider is one of the biggest and most complex scientic instruments of our time, designed to elucidate the mechnism of electroweak symmetry breaking in the Standard Model of particle physics. This mechanism provides mass to the heavy gauge bosons and would result in a yet not discovered particle: the Higgs boson. Establishing or excluding the Higgs boson would be a major leap forward in High Energy Physics. At the time of writing, the CMS Collaboration is closing in on the detection or exclusion of this new particle. The discovery of the Higgs particle would be by no means the end of the story, since the Standard Model does not give any clue why the mass of the Higgs boson would be the value required by the current experimental constraints. Supersymmetry is a candidate framework to extend the Standard Model and would stabilize the mass of the Higgs boson. This theory predicts the existence of a supersymmetric partner particle for each of the existing Standard Model particles. This thesis describes the search for these new particles in proton-proton collisions recorded in 2010 with the LHC. The jets and missing transverse energy search for Supersymmetry is one of the most sensitive channels to look for these supersymmetric particles. This inclusive analysis is based on measuring very precisely the Standard Model backgrounds and looks for an excess of events. One of the largest backgrounds is the Z(vv )+jets production. In this thesis this background is estimated from data using photon + jet events, exploiting the electroweak correspondence between the photon and the Z-boson at high momenta. To study these possible physics processes, which have very low cross sections, an enormous amount of proton-proton collisions needs to be analysed. Since not all collisions can be stored on tape to be investigated, a two-level trigger was designed to select "online" the most interesting events. The muon trigger relies on dedicated muon timing detectors: Resistive Plate Chambers (RPCs), which not fully in place for the first run of LHC in 2010. In this thesis different upgrade scenarios for the RPC trigger have been studied. The outcome of this study was decisive for the RPC upgrade that will be installed in the first long shutdown of LHC.