New eco-friendly gas mixture for Resistive Plate Chambers in CMS in the framework of HL-LHC

The Compact Muon Solenoid (CMS) experiment at CERN is a multi purpose particle detector designed to make accurate measurements on a wide range of physics topics. Within the coming framework of High Luminosity-LHC an increased amount of background events is expected to be recorded with the normal operation of the machine. In order to keep the high accuracy and precision of the recorded measurements, a general upgrade to the systems has been going on since the last couple of years. The Resistive Plate Chambers are part of the general Muon Detector which works with a standard gas mixture of 95.2\% C2H2F4 which accounts for the number of primary ion-electron pairs, 4.5\% iC2H10 that allows to avoid photon feedback effects and 0.3\% SF6 which is an electron quencher. C2H2F4 and SF6 are very well-known Greenhouse gases with Global Warming Potential (GWP) of 1430 and 22600, respectively. During the Run 2 of LHC major leakages were produced at detector level, and due to the increasing costs of the Freon in the EU, CERN has actively started a search for alternatives to replace the main active medium, identifying based CO2 gas mixtures as the main possible candidate for a short-mid term solution. On this report an analysis is presented for the results obtained for four different CO2 based gas mixtures with different concentrations of SF6 in the presence of both a muon beam accounting for the signal and a gamma background radiation source. The results showed a good performance for all four candidates, but the selection of a final candidate is not yet presented as more studies are currently on their way to investigate the aging effects of each one of them.