Protonium X-ray spectroscopy

The Lyman and Balmer transitions from antiprotonic hydrogen and deuterium were studied extensively at the Low-Energy-Antiproton Ring LEAR at CERN in order to determine the strong interaction effects. A first series of experiments was performed with semiconductor and gaseous X-ray detectors. In the last years of LEAR operation using a Bragg crystal spectrometer, strong interaction parameters in the 2p states of antiprotonic hydrogen and deuterium were measured directly. The results of the measurements support the meson-exchange models describing the medium and long range part of the nucleon-antinucleon interaction.