The EPSI R&D: development of a X-ray detector for the detection of synchrotron radiation in space

The direct measurement of the antimatter components in cosmic rays provides a crucial information on the mechanisms responsible for their acceleration/propagation and represent a powerful tool for the indirect search of dark matter. To date, charge sign discrimination has been performed by the use of magnetic spectrometers, which are not suited to extend the current measurements above a few hundreds of GeV in a relatively short time scale. Since most of present and future experiments dedicated to the high energy frontier in space are based on large size calorimeters, it would be important to develop an alternative charge sign discrimination technique that can be integrated with them. The Electron Positron Space Instrument (EPSI) project is a two year R&D aiming to study the feasibility of electron/positron separation in space by exploiting the synchrotron photons emitted as the charged particles travel in the geomagnetic field. The simultaneous detection of the lepton with an electromagnetic calorimeter and its synchrotron photons with a X-ray detector is enough for charge sign discrimination. This technique requires the development of a X-ray detector optimized to have a high detection efficiency down to the keV region, while keeping the cost low enough to make it scalable to a large area. After a short introduction about the project motivations and goals, in this contribution we describe the activities relative to the optimization of the single cell of the X-ray detector.