Aging Study of the CMS ME0 Triple-GEM Detector for the HL-LHC Upgrade

The CMS ME0 Triple-GEM detector will operate in the high-background forward region of the HL-LHC and therefore requires validation of its stability under large accumulated charge. An accelerated X-ray aging study is presented for a localized sector of an ME0 detector with an irradiated area of 67.6 cm$^2$, operated with an Ar/CO2 (70/30) gas mixture. The irradiation was performed using an X-ray source at 40 kV and 80 $\\mu$A, while detector performance was monitored through periodic effective-gain measurements with temperature and pressure corrections applied. The expected accumulated charge for 10 years of HL-LHC operation corresponds to 7.9 C/cm$^2$, and the study is ongoing toward 15.8 C/cm$^2$. To date, the irradiated sector has accumulated 9.419 C/cm$^2$ over 141.6 h. The temperature and pressure corrected effective gain variation remained within 22.3% (relative standard deviation) across the full accumulated-charge range. No significant gain degradation was observed within the present exposure range. These results support the operational robustness of the CMS ME0 Triple-GEM detector and provide an important step toward its qualification for HL-LHC Phase-2 running.