Voir en


LS2 Report: 144 new muon detectors in CMS

CMS now has a new layer of detectors: 144 gas electron multiplier (GEM) chambers have been installed to detect the muons produced in the very forward region of CMS

CMS last GEMs installation
The last installation of Gas Electron Multiplier (GEM) detectors on the second CMS endcap took place in September. (Image: CERN)

The CMS collaboration has just finalised the installation of its new muon detectors in the outermost layer of the CMS detector: the endcaps. In total, 72 modules, each containing two gas electron multiplier (GEM) detectors, have been inserted into the CMS detector in order to detect muons that scatter at an angle of around 10° in relation to the beam axis. “Half of these modules were put in place in one endcap at the end of 2019,” says Archana Sharma, project leader of the GEM detector project. “And our team, led by GEM Technical Coordinator Michele Bianco, just finalised the installation of the remaining 36 modules in the other endcap, despite the rather challenging circumstances of the COVID-19 pandemic.”

With installation complete, the next step is to fully commission the GEMs of both endcaps, which involves several steps: each detector has to, once again, go through rigorous tests of the operating characteristics. Thus, any possible damage that might have occurred during transportation and installation can be immediately spotted and repaired as needed. The detectors’ basic parameters – no leaks, stable voltages, low background noise, measured connectivity, and the operational characteristics of the electronics – will be set to optimal settings. “We will then proceed with data taking under safe conditions with cosmic rays, initially in local standalone mode and eventually with global running in CMS,” adds Archana Sharma. “We have a lot of work in front of us, but the CMS GEM team is very much up to the task.”

288 additional GEM chambers will be installed during the 2023-2024 year-end technical stop. Then, during Long Shutdown 3 (between 2025 and 2027), 216 more chambers will be added. Nearly 650 new muon detectors spread over three stations will search for the muons that will be produced in the very forward region of CMS in the High-Luminosity LHC (HL-LHC) era, due to start at the end of 2027.


For more information about the GEM detector project, visit the CMS website: https://cms.cern/