Development and performance of Micropattern Gaseous Detectors for the CMS muon system upgrade

The thesis is developed in the framework of the upgrade of the muon system of the Compact Muon Solenoid (CMS) experiment. The CMS muon system is mainly devoted to three functions: muon identification, momentum measurement and triggering. During the first period of operation (Run 1) of the Large Hadron Collider (LHC), these purposes were achieved with three different kinds of gaseous detectors: Drift Tubes (DT) in the barrel, Cathode Strip Chambers (CSC) in the endcaps and Resistive Plate Chambers (RPC) as complementary technology in both the regions. This configuration obtained excellent results during Run 1, but it will be deeply affected by the foreseen increase in luminosity, which will cause a huge increase in the rate of particles produced, and then of the pileup, and of the radiation background. The CMS Collaboration started then an upgrade program, aimed at improving the actual system and completing it with new detectors. For the muon system, interventions both on the chambers themselves and their electronics will be performed. New stations of detectors will be installed in the so-called high eta region, characterized by the highest particle fluxes and the worst background environment. This region was suffering during Run 1 from lack of redundancy, as the technologies available at the time of the installation were not considered able to cope with the high rates and high background characteristic of those regions. For the upgrade, the Collaboration decided to consider also a new generation of gaseous detectors, called Micropattern Gaseous Detectors (MPGDs), which are in general characterized by a higher rate capability, space resolution and resistance to radiation with respect to classical gaseous detectors. The proposed MPGD stations are three, called GE1/1, GE2/1 and ME0; so far, only GE1/1 has been approved for the installation, while the other two are still under discussion. The MPGD technology selected for the GE1/1 station is Gas Electron Multiplier (GEM) detector, while for the other two stations newer generations of MPGD are also being considered by the Collaboration. The work presents in detail the motivations of the upgrade and in particular of the installation of the new stations. The Triple-GEM technology, selected for the GE1/1 station, is completely described and the performance obtained by the Collaboration during the dedicated R&D program are presented. Great attention is given to the analysis of the behavior of Triple-GEM detectors in a radiation environment. Moreover, the structure of the Detector Control System (DCS) of the GE1/1 stations, dedicated to the remote control and monitoring of the detectors installed in the CMS cavern, is described in detail. In the last part of the work, the optional technologies considered for the installation in the other two MPGD stations, uRWELL and Fast Timing Micropattern Detector (FTM) for GE2/1 and ME0 respectively, are presented. In particular, the development of the new prototypes for the ME0 station is described, together with the first performance achieved.