Experiments on Laser-Induced Radiative Formation of Antihydrogen Atoms.

Spectroscopy of antihydrogen and hydrogen atoms can provide a direct test for CPT invariance and the Weak Equivalence Principle, and perhaps also offer insights to searches for new physics. As a step towards that goal, we report on the ATHENA Collaboration's experiments on laser-induced radiative formation of antihydrogen. In this process, i.e. $e^++\bar {p}+\gamma \to \bar {H}+\gamma $ a positron and an antiproton are induced to form a bound state of antihydrogen by using a photon of a specific wavelength. Our main objective is to use a CW $^{13}$C$^{18}$O$_{2}$ laser to induce the formation of antihydrogen atoms with the principal quantum number n = 11. Control of the quantum states of antihydrogen will be necessary for future experiments. This experiment has been performed at the CERN Antiproton Decelerator facility.