ACCELERATOR RELATED BACKGROUND IN THE CMS DETECTOR AT LHC

Complete calculations of the accelerator related background in the muo n spectrometer of the CMS detector at the Large Hadron Collider are pr esented. The simulations have been performed with the STRUCT multi-tur n tracking code and the MARS and FLUKA cascade codes taking into accou nt latest information of the LHC lattice, vacuum conditions, beam clea ning system and the shielding and layout of the CMS experiment. Beam l oss distributions in the interaction regions and their vicinities and their contribution to the background levels in the muon spectrometer o f CMS are analyzed. The studies show that hadronic and electromagnetic components of machine background are efficiently suppressed by the pr oposed CMS shielding, High energy muons penetrate through the shieldin g, but in positions of significance they do not contribute more than a few percent compared to the background generated by the pp-collisions . It is anticipated that the relative contribution of accelerator back ground will be higher during the first years of operation, but will dr op down with the LHC performance evolution. The obtained results conce rning the machine background and the efficiency of the proposed shield ing are rather generic and can be directly applied to the ATLAS detect or.