ANTIHYDROGEN PRODUCTION AND PRECISION EXPERIMENTS - THE ATHENA COLLABORATION

The study of CPT invariance with the highest achievable precision in a ll particle sectors is of fundamental importance for physics. Equally important is the question of the gravitational acceleration of antimat ter. In recent years, impressive progress has been achieved at the Low Energy Antiproton Ring (LEAR) at CERN in capturing antiprotons in spe cially designed Penning traps, in cooling them to energies of a few mi lli-electron volts, and in storing them for hours in a small volume of space. Positrons have been accumulated in large numbers in similar tr aps, and low energy positron or positronium beams have been generated. Finally, steady progress has been made in trapping and cooling neutra l atoms. Thus the ingredients to form antihydrogen at rest are at hand . We propose to investigate the different methods to form antihydrogen at low energy, and to utilize the best of these methods to capture a number of antihydrogen atoms sufficient for spectroscopic studies in a magnetostatic trap. Once antihydrogen atoms have been captured at low energy, spectroscopic methods fan be applied to interrogate their ato mic structure with extremely high precision and compare it to its norm al matter counterpart, the hydrogen atom. Especially the 1S-2S transit ion, with a lifetime of the excited state of 122 ms and thereby a natu ral linewidth of 5 parts in 10(16) offers in principle the possibility to directly compare matter and antimatter properties at a level of 1 part in 10(18). Additionally, comparison of the gravitational masses o f hydrogen and antihydrogen, using either ballistic or spectroscopic m ethods, can provide direct experimental tests of the Weak Equivalence Principle for antimatter at a high precision.