Abstract
The CMS collaboration considers upgrading the muon forward region which is particularly affected by the high-luminosity conditions at the LHC. The proposal involves Gas Electron Multiplier (GEM) chambers, which are able to handle the extreme particle rates expected in this region along with a high spatial resolution. This allows to combine tracking and triggering capabilities, which will improve the CMS muon High Level Trigger, the muon identification and the track reconstruction. Intense R&D has lead to the development of several GEM prototypes and associated detector electronics which were operated in several test beams. Strip cluster parameters, detection efficiency, and spatial resolution for charged particles are studied with position and high voltage scans and at different inclination angles. A first GEM station is foreseen to be already installed in LHC Phase-I to operate jointly together with the existing CSC detectors in the forward region. The resulting improved transverse momentum assignment and lower trigger fake rate will reduce the needed bandwidth and therefore allow to lower the trigger threshold resulting in an increased sensitivity in channels triggering on soft muons, such as H to tau's with subsequent leptonic decays to muons. Further GEM detectors are proposed for LHC Phase-II to significantly increase the forward muon acceptance.
Highlights
The CMS muon system[1] is designed to provide robust, redundant and fast identification of the muons traversing the system, in addition to trigger capabilities and momentum measurement
Precision measurements are provided by Drift Tubes (DT) in the barrel, covering acceptances up to |η| < 1.2 and Cathode Strip Chambers (CSC) in the endcaps covering 1.0 < |η| < 2.4
The performance of the CMS triple-Gas Electron Multiplier (GEM) has been evaluated both in the RD51 lab at CERN with xray sources and in many test beam campaigns with pion/muon beams at the CERN SPS [11] and more recently at FNAL
Summary
The CMS muon system[1] is designed to provide robust, redundant and fast identification of the muons traversing the system, in addition to trigger capabilities and momentum measurement. One of the main goals during the upgrade phases will be to restore the originally foreseen redundancy in the forward region beyond |η| > 1.6 based on modern, high-resolution and fast gas detectors capable of fully exploiting the increased LHC performance [2] and sustaining reliable operation for the decades. Such detectors have to satisfy a high rate capability, O(MHz/cm2), a good time resolution for triggering, and a good spatial resolution, O(100 μm), for tracking. There are various solutions in the field of micro-pattern gaseous detectors (MPGDs), the gaseous electron multipliers (GEMs) [3]
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