The simulation of the CMS silicon tracker

The CMS Tracker is the largest build all silicon tracking detector ever made. It consists of 201 m² of silicon strip detectors, already assembled, and 1 m² of silicon pixel detectors expected to be assembled by Fall 2007. A total of 1440 pixel and 15148 microstrip modules are mounted in several substructures for a total of about 66 million and 9 million readout channels, respectively. The design and the physics analysis potential depend on the accuracy of the simulation of such a complex device. The fast shaping times of the electronics and the signal degradation due to the harsh radiation hardness of the LHC demand careful simulation of its response. The accuracy of the predicted space point resolution depends on the ability to correctly model several factors: the diffusion of charges in the 4 T magnetic field of CMS, the delta ray emission, the inter-strip capacitance, the collected charge and the noise. In addition, a detailed description of the positioning of the detectors is demanded. The large number of channels implies a substantial passive material to readout, power and cool the electronics. This causes multiple scattering, nuclear interactions, electron bremsstrahlung and photon conversions, that in turn demand an accurate evaluation of the passive material budget.