FEMTOMETER TOROIDAL STRUCTURES IN NUCLEI

The two-nucleon density distributions in states with isospin T=0, spin S=1, and projection M(S)=0 and +/- 1 are studied in H-2, He-3,He-4, L i-6,Li-7, and O-16. The equidensity surfaces for M(S)=0 distributions are found to be toroidal in shape, while those of M(S)=+/-1 have dumbb ell shapes at large density. The dumbbell shapes are generated by rota ting tori. The toroidal shapes indicate that the tensor.correlations h ave near maximal strength at r<2 fm in all these nuclei:. They provide new insights and simple explanations of the structure and electromagn etic form factors of the deuteron, the quasideuteron model, and the dp , nd, and alpha d L=2 (D-wave) components in He-3, He-4, and Li-6. The toroidal distribution has a maximum-density diameter of similar to 1 fm and a half-maximum density thickness of similar to 0.9 fm. Many rea listic models of nuclear forces predict these values, which are suppor ted by the observed electromagnetic form factors of the deuteron, and also predicted by classical Skyrme effective Lagrangians, related to Q CD in the limit of infinite colors. Due to the rather small size of th is structure, it could have a revealing relation to certain aspects of QCD. Experiments to probe this structure and its effects in nuclei ar e suggested. Pair distribution functions in other T,S channels are als o discussed; those in T,S= 1,1 have anisotropies expected from one-pio n-exchange interactions. The tensor correlations in T,S=0,1 states are found to deplete the number of T,S=1,0 pairs in nuclei and cause a re duction in nuclear binding energies via many-body effects.