Testbeam results for full-size triple GEM detectors

The High Luminosity LHC (HL-LHC) will provide exceptional instantaneous and integrated luminosities. The forward region $\mid \eta \mid \ge 1.5$ of the Compact Muon Solenoid (CMS) detector will face extremely high particle rates in tens of $KHz/cm^2$ and hence it will affect the momentum resolution and longevity of the muon detectors. To overcome these issues the CMS-GEM collaboration has proposed to install new large size rate capable Triple Gas Electron Multiplier (GEM) detectors in the forward region of CMS muon system. The first set of Triple GEM detectors will be installed in the GE1/1 region $(1.5 \le \eta \le 2.2)$ of muon endcap during the long shutdown 2 of the LHC. Towards this goal, full size CMS Triple GEM prototype chambers have been fabricated and put under the test beam at the CERN SPS test beam facility. The GEM detectors were operated with two gas mixtures $Ar/CO_2$ (70/30) and $Ar/CO_2/CF_4$ (40/15/45). In 2014, good quality data was collected during test beam campaigns. In this paper, the performance of the detectors is summarized based on their tracing efficiency and time resolution.