Gamma Background Simulation for the RPC Endcap and Barrel regions of CMS/LHC using GEANT4

We present results for the CMS-RPC sensitivity to gamma rays which were simulated with GEANT4 Monte-Carlo Code. The simulations were performed as a function of gamma energy in a range from 0.007 to 1000 MeV. In order to evaluate the γ-induced rates in the CMS muon system, the gamma spectra expected in the CMS endcap and barrel regions were taken into account. The estimated rates induced by an isotropic gamma source in the ME1, ME2, ME3, and ME4 were 138.0, 42.0, 29.0, and 28.0 Hz/cm2, respectively, when the GEANT4 standard electromagnetic package was used for the simulations. Whereas, the hit rates estimated for the MB1 and MB4 stations were ∼ 0.4 and 1.26 Hz/cm2, respectively, when the same gamma-ray source and the same GEANT4 package were employed for the simulatiom.