CERN Accelerating science

CMS Note
Report number	arXiv:2201.09021 ; CMS-CR-2021-268
Title	Rate capability of large-area triple-GEM detectors and new foil design for the innermost station, ME0, of the CMS endcap muon system
Author(s)	Bianco, Michele (CERN) ; Fallavollita, Francesco (CERN) ; Fiorina, Davide (INFN, Pavia) ; Pellecchia, Antonello (INFN, Bari) ; Garcia, Luis Felipe Ramirez (Antioquia U.) ; Rosi, Nicole (Antioquia U.) ; Verwilligen, Piet (INFN, Bari)
Collaboration	CMS Collaboration
Publication	2021-10-16
Imprint	25 Nov 2021
Number of pages	5
In:	IEEE NSS MIC 2021, Online, Japan, 16 - 23 Oct 2021, pp.CMS-CR-2021-268
DOI	10.1109/NSS/MIC44867.2021.9875626
Subject category	Detectors and Experimental Techniques
Accelerator/Facility, Experiment	CERN LHC ; CMS
Abstract	To extend the acceptance of the CMS muon spectrometer to the pseudorapidity region (2.4,2.8), stations of triple-GEM chambers, called ME0, are planned for the CMS Phase 2 Upgrade. These large-area, micro-pattern gaseous detectors must operate in a challenging environment with expected background particle fluxes up to 150 kHz/cm2. Unlike traditional non-resistive gaseous detectors, the rate capability of large-area triple-GEM detectors is limited not by space charge effects, but by voltage drops on the chamber electrodes due to avalanche-induced currents flowing through the resistive protection circuits. We present a study of the irradiation of large-area triple-GEM detectors with moderate fluxes to obtain a high integrated hit rate. The results show drops as high as 40\% of the nominal detector gas gain, which would result in severe loss of tracking efficiency. We discuss possible mitigation strategies leading to a new design for the GEM foils with electrode segmentation in the radial direction, instead of the "traditional" longitudinal segmentation. The advantages of the new design include maintenance of a uniform hit rate across different sectors, minimization of gain-loss without the need for voltage compensation, and independence of detector efficiency on background flux shape.
Copyright/License	preprint: (License: arXiv nonexclusive-distrib 1.0) publication: © 2021-2026 IEEE

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