Prospects for the detection of the chargino-neutralino direct production with the ATLAS detector at the LHC

The Large Hadron Collider (LHC), currently under installation at CERN, is designed to provide high-energy proton collisions at the TeV energy scale, with a large instantaneous luminosity. This will allow to explore an energy region never reached by the previous accelerators and to search for new physics, also beyond the Standard Model (SM), as expected by a wide range of models. ATLAS (A Toroidal LHC Apparatus) is one of the four experiments which will be installed at the LHC. It is a general-purpose experiment which address the investigation of the full discovery potential provided by the LHC. Chapter 1 is dedicated to the description of the accelerator, the ATLAS experiment and its discovery capabilities. ATLAS is a large and complex experiment, accounting roughly $10^8$ electronic channels. Its trigger and data acquisition systems will be able to select and save few interesting events in between millions. Hence, to bring ATLAS to its maximum performances, a complete and effective monitoring system, able to facilitate the reaching of the correct running conditions and the assessing of the data quality, will be needed. The development of such monitoring tools started during the past beam tests and, at present, it continues supporting the detector commissioning and installation phase. In chapter 2, the development of a lightweight low-level monitoring framework, devoted to the hardware-functionality monitoring, is discussed. Presently the SM is not considered as an ultimate theory, and therefore new models are studied in order to find answers to open questions. Among these theories, the supersymmetries provide a framework that can possibly solve some theoretical problems, such as the hierarchy problem. Up to now, no experimental evidences of supersymmetries were found, however, if they exist, the LHC experiments could possibly find their signatures. An introduction to supersymmetrical theories, particularly focused on gaugino physics, is the object of chapter 3. Among the several signatures predicted by the supersymmetric models, the decay of $\tilde\chi_0^2\tilde\chi_1^\pm$ gaugino pairs into three leptons and missing transverse energy is particularly interesting. Indeed this channel has a low SM backgrounds, especially from QCD, and can provide information on the model parameters. Hence, we developed, through fast simulation data, a search strategy for the trilepton channel, within the ATLAS detector, for a large number of models. The results of this analysis are reported in chapter 4. Most of the LHC discovery potential is driven by its large target luminosity of $10^{34}$ cm$^{-2}$s$^{-1}$. However, to reach this target, fine optimizations of beam optics and tuning are necessary. Moreover, experiments may need to know the bunch-by-bunch luminosity, in order to correct physics results for pile-up events. Hence, a luminometer, able to high-precision bunch-by-bunch relative luminosity measurements, will be an effective tool both for the accelerator and the experiments. In chapter 5, the development of a LHC luminometer, based on a fast radiation-hard argon ionization chamber, performed at the Lawrence Berkeley National Laboratory, is discussed.