Aging studies of the triple-GEM detectors for future upgrades of the CMS muon high rate region at the HL-LHC

The high-luminosity LHC (HL-LHC) upgrade is setting a new challenge for particle detection technologies. In the CMS muon system based on gas detectors, the increased luminosity will yield a ten times higher particle background compared to the present LHC conditions. To cope with the high-rate environment and to maintain the actual performance, new Gas Electron Multiplier (GEM) detectors will be installed in the innermost region of the forward CMS muon spectrometer, $\mathrm{2 < \eta < 2.8}$ (ME0 project). The detailed knowledge of the detector performance in the presence of such a high background is crucial for an optimized design and efficient operation at the HL-LHC. A precise understanding of possible aging effects of detector materials and gases is of extreme importance. For this reason, aging tests of full sized triple-GEM detector operated with an $\mathrm{Ar/CO_2 \ (70/30)}$ gas mixture at an effective gas gain of $\mathrm{2 \times 10^4}$, are in course at GIF++, the CERN Gamma Irradiation Facility. One detector is irradiated with $\mathrm{662 \ keV}$ gamma-rays from a $\mathrm{14 \ TBq \ ^{137}Cs}$ source and, in parallel, a second similar detector with $\mathrm{22 \ keV}$ X-rays at the quality control lab. This contribution describes the performance of triple-GEM detectors during the irradiation test and reports on their state-of-the art.