Development of a tracker based on GEM optically readout

The high-resolution tracking of low energy release particles had a remarkable development in recent years and will give a crucial contribution in different sectors, from medical applications to those in dark matter search. Thanks to their characteristics (high space and time resolution, low material budget, large volumes, low costs) the gas detectors have shown to be ideal candidates for this type of trackers. In particular, a very promising technique regards the optical reading of the light produced by the de-excitation of gas molecules during the processes of electron multiplication. This type of detector has been made possible thanks to the great progresses achieved in last years in the performance in micro pattern gas detector and in the evolution of the CMOS technology which led to the production of sensors able of offering high sensitivity and granularity combined with a very low noise level. In this thesis I studied the performance of a two prototypes where the light is produced through the multiplication of electrons in a triple GEM structure and acquired by a camera equipped with CMOS sensor with 4 Mega Pixels. The use of high light yield HeCF4 gas mixture allowed to reveal, for the first time with this technique, the tracks of minimum ionizing particles. The performance of this detector were measured and optimized in laboratory and tested on an electron beam at the Beam Test Facility of the National Laboratories of Frascati.