1. Lee, T. D., and Yang, C. N.’ Phys. Rev., 104, 254 (1956)
2. 2.Wu, C. S., Ambler, E., Hayward, R. W., Hoppes, D. D., and Hudson, R. P., Phys. Rev., 105, 1413 (1957)
3. Christenson, J. H., Cronin, J. W., Fitch, V. L., and Turlay, R., Phys. Rev. Letters, 13, 138 (1964)
4. Lobkowicz, F.’ Melissinos, A. C., Naga- shima, Y., Tewksbury, S., von Briesen, H., and Fox, J. D., Post- deadline paper (GF10) (Am. Phys. Soc., Washington Meeting, 1966 )
5. Kinoshita, T., Phys. Rev. Letters, 2, 477 (1959)