Tests of a phenolic four-gap RPC with cosmic muons and high-rate gammas for CMS/LHC experiment

We report a systematic study of detection rate capability of phenolic four-gap resistive plate chamber (RPC) in use of high-energy physics experiments. In the current study, a prototype phenolic four-gap RPCs were tested for cosmic muons and gamma rays irradiated by a 150 mCi ¹³⁷Cs source. The efficiency plateau of cosmic muons measured by the four-gap RPCs with a proper threshold was about 600 V. Furthermore, the shift in the operation high voltage caused by a gamma rays background rate of 3.0 kHz cm^-2 was measured as about 400 V, which was smaller than the size of the measured muon efficiency plateau. We conclude from the present study that the four-gap RPCs are capable of high-rate triggers in high-η region of the CMS experiment.