Triple-Gas Electron Multiplier technology for future upgrades of the CMS experiment: construction and certification of the CMS GE1/1 detector and longevity studies

This Doctoral Thesis takes place in the framework of the upgrade of the Muon System of the Compact Muon Solenoid (CMS) experiment. To extend the sensitivity for new physics searches, a major upgrade of the LHC machine has been decided and is being prepared, the High Luminosity LHC (HL-LHC). The increase of the energy and luminosity during the future upgrades of the LHC machine will deeply affect the performance of the CMS Muon System due to the harsh background environment and the high pile-up. In order to cope with very high operation condition, high pile-up and background environment in particular in the forward region, the CMS Collaboration is planning to install a detector based on the Gas Electron Multiplier (GEM) technology to upgrade the CMS Muon System, instrumenting the non-redundant CMS high $\eta$ region with detectors that could withstand the hostile environment and high luminosity rates at the LHC and its future upgrades. The Doctoral Thesis subject has been proposed by the CMS GEM Collaboration and three main research projects have been conducted in this context. The first project, conducted in the framework of the LS2 GE1/1 detector mass production, is focused on the production and quality control of the triple-GEM detectors for the CMS-GE1/1 station, to be installed in the CMS Muon System during the second Long Shutdown in 2019/2020. The aim of the LS2 GE1/1 detector mass production is to assembly, certify and characterize the CMS GE1/1 triple-GEM detectors using the large amount of data acquired during the 18 months of quality certification tests at the CERN production site. The second project has been focused on the long-term operation of triple-GEM detectors, in particular the study of the aging phenomena. Aging is one of the most critical limitations of the use of gaseous detectors in strong radiation environments; it includes all the processes that lead to a significant and permanent degradation of the detection performences: gain drop, non-uniformity, dark current, discharge, etc. Similarly to several gaseous detector, the triple-GEM detector might be subject to aging effect when operating in a high-rate environment. For this reason, several aging tests of full size CMS-GE1/1 triple-GEM detectors have been carried out in parallel at CERN Gamma Irradiation Facility (GIF++), using for the irradiation an intense $14~TBq~(2015)~^{137}Cs$ source emitting $662~keV~\gamma$-$rays$, and at the CMS-GEM QA/QC Lab. using as irradiation source a $22~keV~X$-$rays$ source. The third project included a systematic investigation of the discharge probability with the triple-GEM detectors under neutron irradiation. Still on the subject of the capability of the new detectors of working in intense neutrons and photons environment, the CMS-GEM Pavia group performed several neutron tests at CERN CHARM (Cern High energy AcceleRator Mixed Field facility). The aim of these neutron tests has been the study of neutron sensitivity and neutron-induced discharge probability of a triple-GEM detector irradiated by neutrons. These measurements have been crucial in the choice of technology to be installed on the detector in order to preserve adequate detector performance and its discovery potential in high luminosity environment of the HL-LHC era. The aging and the discharge probability studies have been performed in the framework of an $R\&D$ activity on detectors for the innermost region of the forward muon spectrometer of the CMS experiment. These long-term operation test campaigns have demonstrated the robustness and the radiation hardness of the triple-GEM technology, which could tolerate the radiation dose foreseen in 10 HL-LHC years of operation in the ME0 environmental of the CMS experiment. Therefore, the triple-GEM technology, based on the single-mask photolithography technique produced by the CERN PCB workshop, is fully validated for CMS-ME0 upgrade project. The results obtained during the three years of Ph.D. have been contributed to the success of the CMS-ME0 upgrade project and its approval by the CMS and LHCC Collaboration.