1. For a review see R. Bizzarri, in Proceedings of the Symposium on Antinucleon-Nucleon Annihilations, Chexbres, 1972, (CERN 72–10, ed. L. Montanet), p. 161 and references therein
2. G. Bassompierre et al., in Proceedings of the 4th European Antiproton Symposium, Barr-Strasbourg, France, 1978 (ed. E. Friedman), (CNRS, Paris), Vol. 1, p. 139
3. S. Devons et al., Phys. Rev. Lett. 27, 1614 (1971)
4. O. D. Dalkarov, B.O. Kerbikov, and V.E. Markushin, Yad. Fiz. 25,853 (1977)
5. O. D. Dalkarov, B.O. Kerbikov, and V.E. Markushin, (Sov. J. Nucl. Phys. 25, 455 (1977))