Studies of eco-friendly gas mixture for RPC detectors at CERN LHC experiments.

The resistive plate chamber (RPC) detectors at CERN LHC experiments are operated with a freon-based gas mixture, containing $C_{2}H_{2}F_{4}$ and $SF_{6}$, both greenhouse gases (GHG) with a very high global warming potential. The European Union defines a set of regulations aiming at reducing the GHG emissions from fluorinated gases. These regulations could bring lower availability and higher costs in the future. The aim of this contribution is to study new eco-friendly gas mixtures that are compatible with the current CERN RPC systems and that allow a good detector performance. Some alternatives to $C_{2}H_{2}F_{4}$ and to $SF_{6}$ were tested, such as $CO_{2}$, He, $HFO1234ze$ and Novec 4710. First, a characterization with cosmic muons was done by evaluating the detector efficiency, currents, streamer probability, prompt charge, cluster size and time resolution. Then, the RPC performance was evaluated at CERN Gamma Irradiation Facility where a $12 {TBq} ^{137}Cs$ source and a muon beam allow to simulate the LHC experiment radiation background. The substitution of $30%$ R134a concentration with He or $CO_{2}$ does not imply any change in RPC performance. Moreover, the Novec 4710 is promising as a $SF_{6}$ substitute with $0.1%$ concentration.