Highlights on Searches for Environmentally Friendly Gases in the CMS RPC System

The Resistive Plate Chambers (RPC) of the Compact Muon Experiment (CMS) experiment at the Large Hadron Collider (LHC) operates with a gas mixture composed of 95.2$\%$ of C$_2$H$_2$F$_4$, a greenhouse gas with high Global-Warming Potential (GWP). In recent years, several eco-friendly alternatives, such as hydrofluoroolefins (HFOs), have been investigated to identify sustainable replacements that preserve the detector performance. Another promising approach is to partially replace C$_2$H$_2$F$_4$ with CO$_2$, reducing the mixture's GWP by 30–40$\%$. These studies are being performed at the CERN Gamma Irradiation Facility (GIF++), which replicates the radiation conditions expected during the High-Luminosity Phase-2 data taking at the Large Hadron Collider (HL-LHC), using an 11.5 TBq gamma source and a muon beam. Updated results are presented on the performance of two 1.4 mm double-gap RPC chambers operating with various alternative gas mixtures under high-rate gamma irradiation. Results are also presented on RPC aging studies with these alternative gas mixtures, providing a deeper insight into the long-term performance and stability for the future of the RPC muon system.