Positronium production in thin porous films to study antimatter at CERN

The interest of the present work is related mainly to the AEgIS experiment at CERN. An efficient formation of cooled positronium (Ps) atoms is a requisite for the production of antihydrogen in the AEgIS experiment. It is proposed the development of engineered porous silica films to produce Ps in transmission for the first time. The new transmission geometry would be decisive to improve the statistic for antihydrogen formation. Silica based mesoporous materials are extensively investigated since a high fraction of the implanted positrons form Ps inside them. Ps is emitted in this porous materials with high kinetic energy (1-3 eV). Ps cooling is necessary to form antihydrogen. Ps loses its kinetic energy and cools down by means of collisions with the walls of the pore. The AEgIS experiment will be performed at cryogenic temperatures (about 100 mK). At these temperatures, even in ultra high vacuum conditions, ice formation in normal silica is documented. Ps diffusion is inhibited by ice formation. For this reason the pore surface of the new proposed materials is development with hydrophobic patches to avoid ice formation at low temperature.
The measurements to characterize the new materials will be performed with a variable energy positron beam at cryogenic temperature up to room temperature.

• AEgIS (Antihydrogen Experiment: gravity, Interferometry, Spectroscopy)
• AEgIS (CERN)
• Positron Laboratory VEPAS (Politecnico di Milano)

• AEgIS (Milan Group)

• http://www.como.polimi.it/positron

• http://www.mi.infn.it/~trezzi/people.htm