GEM Detectors for the Upgrade of the CMS Muon Spectrometer

The Large Hadron Collider (LHC) will be upgraded in several phases to allow a significant expansion of its physics program. We are nearing the end of Long Shutdown 2 (LS2, 2019-2021), after which the LHC will initiate its third running period (Run-3) expected to last three years. In Run-3 LHC will collide protons with an instantaneous luminosity of 2-3×10$^{34}$cm$^{−2}$s$^{−1}$ exceeding its design luminosity by a factor of 2-3, allowing the CMS experiment to collect an integrated luminosity of approximately 100 fb$^{−1}$/year. A subsequent upgrade in 2025-27 (Long Shutdown 3 - LS3) will increase the luminosity up to 5×10$^{34}$cm$^{−2}$s$^{−1}$. The CMS muon system must enable a physics program that maintains sensitivity for electroweak measurements and for Beyond the Standard Model searches, similar to what was achieved in Run-1 and Run-2. To cope with the corresponding increase in trigger rates and to provide additional coordinate measurements in the high background environment, the installation of additional sets of muon detectors, referred to as GE1/1, GE2/1 and ME0, that use Gas Electron Multiplier (GEM) technology, has been approved. The GE1/1 chambers have already been installed in spring-summer 2020 and are currently being commissioned and tested with cosmic rays. The construction of GE2/1 will start in 2021, while for ME0 the final R&D; is in progress and construction is foreseen in 2023. We present an overview of the Muon Spectrometer upgrade using the GEM technology, the performance of the GE1/1 chambers during Quality Control tests and in cosmic ray tests, and the design of the GE2/1 and ME0 chambers.