I. Endo, K. Baba, H. Fujii, Y. Sumi, S. Anami, S. Ninomiya, S. Kato and A. Murakami: Phys. Letters 47B, 469 (1973); H. Fujii: Journal of Science of the Hiroshima University A40, 1 (1976).
For more details of this experiment see Y. Sumi: Proc. INS Symposium on Electron and Photon Interactions, ed. by S. Homma, 190 (1975).
T. Fujii, T. Kondo, F. Takasaki, S. Yamada, S. Homma, K. Huke, S. Kato, H. Okuno, I. Endo and H. Fujii: Phys. Rev. Letters 28 (1972) 1672 and 29 (1972) 244(E), see also INS-Report-256 (1976).