Radiation damage study on innovative silicon sensors for the CMS tracker upgrade

Throughout the last decades, High Energy Physics aims have shifted towards the search for evidence of events able to confirm or dismiss different physical models which all have proven able, to a certain extent, to give a reliable description of the laws governing the universe. Such models (Standard Model, Super Symmetric Theory, and so on) provide comparable predictions in the low-energy scale, starting to diverge only at energy scales of the order of hundreds or even thousands of GeV. For this reason, the latest developments in HEP experiments have seen the realization of massive colliders (starting from the Tevatron, going through the LEP and ending up to the LHC), able to provide particle beams of energies ranging from some hundred GeV up to several TeV. The current generation of experiments at LHC is expected to receive an integrated dose which, at the detectors closer to the interaction point, will reach levels of 10^6 Gray, corresponding to an equivalent hadron fluence of up to 3e15 neq/cm2. None of the tracking detector technologies presently used in the LHC can survive those levels of radiation, hence replacements of the inner tracking layers have been scheduled since the design stage of the experiments. Outer layers are going to suffer less from radiation exposure, but are as well realized with technologies with lower radiation hardness. For this reason, R&D campaigns are in progress, aimed at the development of new radiation hard detector technologies, to be used for a luminosity upgrade of the detector systems. For all the current experiments at LHC, the inner tracking systems are realised with silicon detectors (pixel, strips, drift detectors). The choice of silicon detectors is made natural by their superior performances in terms of spatial resolution, signal collection time and radiation hardness. Though some alternatives have been proposed (e.g. diamond detectors), silicon will rule the scenes for the next generation of tracking detectors, given several practical considerations that will emerge in the following chapters. Moreover several technologies have been developed to improve the radiation hardness of silicon detectors, providing up to now excellent results. The work presented here is a contribution to this R&D eort, aiming to study, characterize and analize, with the highest detail possible, the physical microscopical processes that allow some kind of silicon technologies to show radiation hardness characteristics that were not conceivable at the time when the first generation of silicon detectors for LHC was built.