1. J.J. Aubert et al. Phys. Rev. Letters 33, 1404 (1974). See also e+e− Physics, same proceedings, by H.F. Schopper.
2. M. Chen, Lecture at International Summer Institute in Cargèse on “Weak and Electromagnetic interactions at High Energies” published by Plenum Press, 1976, Editor M. Levy.
3. B.C. Brown et al., FNAL preprint (1977).
4. K.J. Anderson et al., Phys. Rev. Lett. 36, 237 (1976).
5. B. Knapp et al., Phys. Rev. Lett. 34, 1044 (1975).