Systematic study of RPC performances in polluted or varying gas mixture compositions: An online monitor system for the RPC gas mixture at LHC

A correct gas mixture composition is fundamental for proper and safe operation of the Resistive Plate Chamber large detector systems. At long term, small changes in the gas mixture composition can alter the RPC performance affecting the data quality in the ALICE, ATLAS and CMS experiments at CERN. A constant monitoring of the gas mixture quality injected in the RPC systems would possibly avoid this kind of problems. A systematic study has been performed to understand the RPC performances with slightly different gas mixture compositions and in presence of common impurities. The systematic analysis of several RPC parameters in different gas mixtures allows the quick identification of variations in the mixture. A set-up for the online monitoring of the RPC gas mixture in the LHC experiment is also proposed.