Performance of new CO 2 based mixture in CMS Improved Resistive Plate Chambers in HL-LHC environment

Resistive Plate Chamber (RPCs) detectors in the Compact Muon Solenoid operate with a gas mixture composed of 95.2% of C 2 H 2 F 4 , which provides a high number of ion-electron pairs, 4.5% of iC 4 H 10 , which ensures the suppression of photon-feedback effects, and 0.3% of SF 6 , used as an electron quencher to further operate the detector in streamer-free mode. C 2 H 2 F 4 is known to be a Greenhouse gas with a global warming potential (GWP) of 1430. Consequently, several ECO-friendly alternatives to C 2 H 2 F 4 have been investigated in recent years. In this context, a short-mid term approach for the upcoming years of Large Hadron Collider (LHC) operation could be to focus on reducing the GWP of the RPC gas mixture by replacing C 2 H 2 F 4 with CO 2 . The studies are conducted at the CERN Gamma Irradiation Facility in the North Area of the Super Proton Synchrotron (SPS), where a 13.6 TBq radiation source and a muon beam from SPS mimic the conditions of Phase-II (i.e. High-Luminosity (HL)) of the LHC. This paper presents the performance of a 1.4 mm gap RPC with three different CO 2 based mixtures (30 and 40% of CO 2 ; 0.5 and 1% of SF 6 ) under high gamma background conditions with the perspectives for the longevity campaign.