DEUTERON RADIUS AND NUCLEAR FORCES IN FREE SPACE

Experimental knowledge and theoretical understanding of the deuteron matter radius are reviewed. An experimental value of rm(exp)=1.9502 (20) fm is found by using the 1962 Stanford data, the 1973 Monterey data and the 1981 Mainz data for the ratio of electron-deuteron to electron-proton elastic scattering cross-sections, plus the 1979 Erevan data and the 1990 Saclay data on electron-deuteron elastic cross-sections. The theoretical radius is dominated by a model-independent part, 1.9557 (7) fm or 1.0028 rm (exp) in magnitude, determined by the triplet scattering length, the deuteron binding energy, and the triplet effective range. The remaining contribution to the theoretical radius is model-dependent. It gives about 0.0110 fm, or 0.0056 rm(exp), for the Bonn potentials which have relatively weak short-range tensor forces. Experiment and theory thus differ by 0.8%. This discrepancy cannot be understood in terms of known physical processes involving relativity, meson exchanges, and abnormal higher-mass components of the wave function. Interestingly, the five experimental results can be separated into two inconsistent groups: (a) The Stanford and Saclay results agree, giving a weighted average of 1.967 (5) fm in agreement with theory. (b) The Monterey, Mainz and Erevan results also agree, giving a weighted average of 1.9488 (21) fm in disagreement with theory. The possibility of obtaining nuclear-size information from atomic Lamb shift measurements is also reviewed. In particular, the latest deuterium-hydrogen isotope shift of the 1S-2S Lamb shift yields a deuteron matter radius of 1.963 (5) fm. New measurements of both deuteron and proton charge radii would be of great interest in both nuclear and atomic physics.