Charged particle detection performance of gas electron multiplier detector for the upgrade of CMS endcap muon system at the CERN LHC

The CMS detector is one of two general-purpose detectors at the CERN LHC. LHC will provide exceptional high instantaneous and integrated luminosities after second long shutdown. The forward region $\mid \eta \mid \geq 1.5$ of the CMS detector will face extremely high particle rates in 10s of kHz/cm2 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 high rate capable triple Gas Electron Multiplier (GEM) detectors in the forward region of CMS muon system. The proposal has been approved recently. The first set of Triple GEM detectors will be installed in the GE1/1 region ($1.6 < \mid \eta \mid < 2.2$) of muon endcap during phase-II upgrade 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:CO2 (70:30) and Ar:CO2:CF4 (40:15:45). There were two extensive data taking campaigns during 2014 during which data was collected with GE1/1 detector. Here, the performance of detector such as efficiency and time resolution is reported.