1. M.C. Abereu, et. al., NA50 Collaboration, Phys. Lett. 530, 43 (2002)
2. R. Szwed, C. Wronchna, Z. Phys. C29, 255 (1985)
3. P. Slattery, Phys. Rev. Lett. 29, 1624 (1972); Phys. Rev. D 7, 2073 (1972)
4. P. Olesen, Phys. Lett. 41B, 602 (1972)
5. G.J. Alner, UA5 Collaboration, Phys. Lett. 160B, 199 (1985)