Production and thermalization of positronium in homogeneous porous silica

Positronium yield using the "3γ method" and lifetime measurements were performed at cryogenic and room temperature by means of a variable energy positron beam in homogeneous porous silica (Aerogel). An estimation of the positronium (Ps) mean diffusion length was obtained by measuring capped samples. An efficient formation of cooled Ps atoms is a requisite for the production of antihydrogen, with the aim of a direct measurement of the Earth gravitational acceleration g of antimatter, which is the primary scientific goal of AEgIS (Antimatter Experiment: gravity, Interferometry, Spectroscopy; CERN, Geneva). Porous materials are necessary to obtain a high Ps yield as well as to thermalize Ps. Our results indicate a high Ps production, long survival time and diffusion length in Aerogel samples. It will be shown that positronium yield, lifetime and diffusion length are independent on temperature and on the effect of gas adsorption at low temperature. The results indicate that Aerogel is a good candidate for an efficient formation of cold Ps for the AEgIS experiment.