1. R. F. Christy andS. Kusaka:Phys. Rev.,59, 405, 414 (1941);J. Mathews:Phys. Rev.,102, 270 (1966);A. N. Mitra:Nucl. Phys. 2, 383 (1956).
2. R. L. Garwin, L. M. Lederman andM. Weinrich:Phys. Rev.,10 5, 1415 (1957).
3. M. Avan andL. Avast:Nuovo Cimento,6, 1500 (1957);G. H. Rawitscher:Phys. Rev.,107, 274 (1957);S. Hirokawa andH. Komori:Nuovo Cimento,7, 114 (1958).
4. W. Frati: Nevis Cyclotron Laboratory Rcport-90 (1960) haso bserved the expected fine structure splitting in the3.D-2P μ-mesic X-rays of Pb. He claims that a spin-3/2 muon would give rise to a third X-ray 0.25 MeV below the doublet and stronger in intensity than either component; since such an X-ray is not observed, he concludes that the possibility of spin 3/2 is ruled out. It is obvious that this conclusion is not free from assumptions concerning the nature of the interaction between the μ-meson and the nucleus.
5. T. D. Lee andC. N. Yang:Phys. Rev.,109, 1735 (1958).