Highly ionising events in silicon detectors

It is shown by simulation studies that essentially each inelastic hadronic interaction in silicon generates a highly-ionising particle (HIP) which can be equivalent to up to 1000 minimum ionising particles (mip) traversing a 500\ mu m silicon detector. However, the probability for events with very high energy deposition drops sharply beyond 100 mip-equivalent. Since the energy spectrum of heavy fragments reaches to few tens of MeV only, the events with highest energy deposition always have to involve several particles. Often these are slow protons which can have ranges up to few centimetres in the detector before the track terminates in a Bragg peak with high energy deposition. Simulation results based on predicted CMS Tracker spectra can be used to predict HIP rates and dead-time in CMS, while simulation results for beam test conditions can be used to compare the simulations with experimental data.