A new approach in simulating RPC and searching for the causes of large cluster size of RPC

The prototype Resistive Plate Chamber (RPC) has been made for the ATLAS phase II upgrade. The beam-test results showed that its cluster size is larger than expected. To figure out the causes, we developed a new approach in simulating RPC which based on Computer Simulation Technology (CST) Suite. The influences from the surface resistivity of the graphite layer and other characteristics have been studied. Comparisons between the simulation data and the beam-tests results have also been performed.