Detector upgrade for the KLOE 2 experiment : The Inner Tracker

A low mass, fully cylindrical and dead region free GEM detector is under development as Inner Tracker for the KLOE experiment upgrade at the DAΦNE facility in Frascati. The proposed detector will play a crucial role in the study of the Ks decays and interferometry. The main physics requirements are: good detector spatial resolution σrφ about 200 μm and σz about 500 μm and a very low material budget inside the active area 1.5 % of radiation length (X0) for the whole detector. The detector consists of five layers of cylindrical triple-GEM detectors (CGEM), covering the space from the beam pipe to the inner cylinder of the KLOE main Drift Chamber. Each layer is realized inserting one into the other the required structure made of 50 μm polyimide foils. The final result is a very light detector with a 0.2 % of X0 per tracking layer inside the active area. After the successful construction and test of a small size prototype 90 mm diameter, 250 mm length, a full scale prototype (300 mm diameter, 352 mm length) of the first layer of the Inner Tracker has been designed and built in all details. We report about the design, construction and some preliminary test of such a large prototype that open the way for a new and competitive category of ultra-light micro pattern gas vertex detector.