One of the most challenging aspects of hadron physics is represented by the proton spin and its interpretation in terms of its internal constituents. The production of a beam of polarized antiprotons would represent a breakthrough in the field, allowing to experimentally access way a series of physics observables related to the proton spin. The PAX Collaboration is performing a series of measurement at the COSY ring to study in detail the mechanisms that could lead to an intense beam of polarized antiprotons.
The PAX collaboration is constructing a large acceptance detector based on silicon tracking telescopes. The developed design is compatible with different experimental activities on the COSY ring: longitudinal spin-filtering, test of time reversal invariance, and, potentially, also deuteron-breakup measurements.