Impact of beam induced backgrounds for the CMS Pixel and other inner radii detectors - Simulation and Data

To determine the radiation environment of CMS, a FLUKA simulation with an updated CMS detector geometry was set up. The radiation field maps from pp-collisions have been calculated for the two limiting energies of LHC, 450 GeV for injection and 7 TeV for nominal LHC collisions. Apart from flux- and dose-maps for the whole CMS cavern, several other quantities are available, some of special interest for the pixel detector, such as the equivalent 1 MeV neutron fluxes and a more detailed radiation damage simulation for the beam condition monitoring system In addition to the pp-collision set up, the beam induced background for the nominal LHC running condition was simulated. For this the contribution from beam halo (collimator tails) as well as the inelastic and elastic beam gas interactions have been simulated separately, so that the impact for the various CMS subdetectors and in particular for the pixel detector can be given as function of beam background contributor. Data from 2009/2010 was taken to benchmark these simulation results, in particular for the near beam pipe detectors, such as the pixels, the beam condition monitors and the hadronic forward calorimeter. The measured data is compatible with the simulation expectation.