Using the pixel detector for fast triggering in CMS

The Standard Model of fundamental interactions (SM) has been extensively tested in many particle experiments during the last 25 years and it has proven to be extremely successful up to the energy scale typical of the weak force. Nevertheless, there is still no experimental evidence of the Higgs boson, one of the key components of the SM, responsible for the breaking of the electroweak symmetry and for the masses of the fermions and of the weak bosons. The Large Hadron Collider (LHC) is scheduled to provide the first proton on proton collision in 2008 at the center of mass energy of 14 Tev, an energy one order of magnitude higher than the regime explored so far. The CMS experiment is an omni-purpose experiment that will operate at the LHC, it will give insight into Standard Model physics and search for physics beyond the Standard Model. In this work we consider the usage of pixel detector information in the reconstruction of hadronic jets in events collected by the CMS detector under high luminosity running conditions, to add a small piece of information to best answer the question of the improvements possible on the physics output of CMS in case of an upgrade of its triggering capabilities. In the first chapter we give a review of the Standard Model and its Minimal Supersymmetric extension. We then summarize the Higgs boson search channels at the LHC and present an update on the current status of Higgs searches at the Tevatron Collider. The second chapter introduces the phenomenology of proton-proton interactions at the LHC and it gives a description of LHC and the CMS experiment, with particular attention to the pixel detector. Chapter three describes a possible application of the pixel detector for triggering at the first level of the CMS trigger. We will first introduce the software frameworks we used for all the simulations, with some details on the tools used in the production of the data samples. In the second part we describe a pixel-based first level trigger and we derive optimized cuts for the selection of the signal of associated production of an Higgs boson with a pair of top quarks. In chapter four we consider a search channel of a Standard Model Higgs boson which could benefit from a reduction of energy thresholds of jet triggers, with the double aim of showing what can be obtained with such search using a sufficient statistics collected by CMS in the running phase of high luminosity, and to show what benefit the channel could receive from a trigger using jets plus pixels. Finally, chapter five gives a summary of the results.