Do unpolarized electrons affect the polarization of a stored proton beam?

Understanding the interplay of the nuclear interaction with polarized (anti)protons and the electromagnetic interaction with polarized electrons in polarized atoms is crucial to progress towards the PAX goal to eventually produce stored polarized autiproton beams at FAIR. Presently, there exist two competing theoretical scenarios: one with substantial spin filtering of (anti)protons by atomic electrons, while the second one suggests an almost exact self-cancellation of the electron contribution to spin filtering. The existing experimental data from the FILTEX experiment allow neither an unambiguous discrimination between the two scenarios nor do they give a direct constraint on the role of the spin-flip scattering in spin filtering. We have started to investigate the depolarization effect of a proton beam stored at COSY injection energy of Tp = 45 MeV by electrons in a 4He storage cell target, as in effect inverse to a polarization buildup by polarized electrons. In this presentation, the experimental realisation including the detector setup (Silicon Tracking Telescopes) and the required COSY machine performance are discussed. (orig.)