Test-Beam Analysis of the Effect of Highly Ionising Particles on the Silicon Strip Tracker

Highly Ionizing Particles (HIPs) created by nuclear interactions in the tracker sensors produce large signals which can momentarily saturate an APV readout chip. This phenomenon is studied in two different beam-tests performed at PSI and X5 in 2002. The probability of a HIP-like event occurring per incident pion is measured, as is the time required for an APV to recover from such an event. Distortions induced in the APV baseline are also studied. From these results, the expected inefficiency of the CMS Tracker due to HIPs is inferred. The dependence of the results on the APV's configuration parameters and inverter stage resistor value is shown.