Production of cold positronium atoms

Positronium will play a primary role in the next generation of antimatter experiments through the following antihydrogen production reaction: (p) over bar + Ps* ->(p) over bare(+) + e(-). In order to study antimatter physical properties (CPT (charge, parity, time) invariance and principle of equivalence test) it is necessary to keep this system at the lowest possible (sub-kelvin) temperatures. This requires the generation of a suitable flux of cold Ps atoms in a vacuum, a non-trivial requirement at the light of the present experimental results. In this paper we discuss the state of the actual knowledge on positronium formation and consequent emission from metallic surfaces and insulators and we show the opportunity to use suitable porous materials to cool positronium through collisions with the inner walls of the pores. We get a rough indication on the geometrical parameters of the pore and we propose a simple experiment to obtain the kinetic energy - and therefore the equivalent temperature - of emitted positronium without using a positron beam.