EPSI R&D: Development of a X-ray space detector for observing the synchrotron radiation from electrons and positrons in the geomagnetic field

Directly measuring the antimatter component in cosmic rays provides crucial information on the mechanisms responsible for their acceleration/propagation and represents a powerful tool for indirect dark matter searches. Charge sign discrimination in cosmic ray experiments has been performed, to date, by the use of magnetic spectrometers, which are not suited to extend the measurements above a few hundreds of GeV in relatively short time scales. It would be therefore important to develop a an alternative charge sign discrimination technique that can be integrated with present and future calorimetric experiments. This is the objective of the Electron Positron Space Instrument (EPSI) project, a two year R&D focused on studying the feasibility of electron/positron separation in space based on the simultaneous detection of the lepton with an electromagnetic calorimeter and its synchrotron emission in the geomagnetic field with a X-ray detector. This requires to develop a X-ray detector optimized to have high detection efficiency in the low energy region, large active area and low cost. In this contribution, after a short introduction to the project’s motivations, we describe the experimental activities regarding the optimization of the single cell of the X-ray detector.