Neutron and photon fluxes and shielding alternatives for the CMS detector at LHC

We present results of a comprehensive simulation study of the neutral particle radiation background around the CMS experiment at LHC. Without shielding these fluxes can reach several MHz/cm2 in the muon system. With our simulated sensitivity of the order of 2% for photons, this implies a signal rate far in excess of that tolerated by a fast trigger system. We show that with a proper shielding the neutral particle rate can be reduced by 1–2, and with some effort, up to three orders of magnitude. We also show that a relatively thin polyethylene moderator is sufficient to protect the central tracker and the preshower detectors against neutron albedo from any of the proposed calorimeter options.