The present and future of the CMS muon system

Abstract The CMS muon system is indispensable for identifying and studying key particles and processes at the LHC. A high-performance muon system not only underpins the discovery potential of CMS but also ensures the precision and reliability required for advancing our understanding of the fundamental laws of nature. The legacy CMS muon detector system, consists of drift tube (DT) chambers in the barrel and cathode strip chambers (CSC) in the end-cap regions, complemented by Resistive Plate Chambers (RPC) in both the barrel and end-cap. During the long shutdown 2 period, Gas Electron Multiplier (GEM) chambers were added in the first station of forward regions to enhance the redundancy of the muon system while maintaining the precision of muon momentum resolution at the Level-1 trigger. Despite increased luminosity and more challenging detector conditions, the CMS Muon system has demonstrated the expected performance in Run 3 across a wide pseudorapidity range. In order to ensure the performance, reliability, and safety of the CMS muon system at the challenging conditions of increased instantaneous luminosity and higher pileup expected during the high-luminosity LHC, simultaneous background and aging studies are being actively conducted. These studies are crucial for understanding the long-term behavior of all muon sub-detectors and helped planning the detector upgrade strategy during the next Long Shutdown 3. This document provides a summary of the results from recent background and aging studies of the CMS muon system and a brief outlook to the future upgrades.