Improving of RPC for Muon System of CMS experiment

In the Endcap regions, CMS Muon spectrometer is using Cathode Strip Chambers (CSCs) as muon tracking and trigger detectors, also Resistive Plate Chambers (RPCs) serve as dedicated trigger detectors and improve the muon reconstruction by providing the excellent timing resolution for identification of muon particles. At the present, the four Endcap discs are not fully equipped: RPCs are covering only Endcap disks up to |ŋ| = 1.8. During the Long Shutdown 3 (from 2023 to 2026) of the Large Hadron Collider, Endcap stations 3 and 4 will be further instrumented with new improved RPCs (iRPCs) that will be covering the pseudorapidly region 1.8 < |ŋ| < 2.4, increasing the redundancy in this region. Nowadays, the final design of RPC chambers has been developed and the RPC double gap prototypes with a gas thickness 1.4mm are being tested. The performance and stability of iRPCs at the future HL-LHC upgrades have been studied (detection efficiency, cluster size, rate capability) at the Gamma-Irradiation Facility (GIF++) at CERN, where high energy charged particle beams (mainly muons) are combined with gammas from a 14 TBq 137Cesium source which simulates the background expected at the CMS experiments. In this paper, the main results obtained during the test at GIF ++ are presented.