Studies of Short-range Structures in Nuclei

Recent, accurate calculations of several nuclei, using quantum Monte Carlo methods and realistic models of nuclear forces, have successfully reproduced many observed properties of nuclei. These calculations have also indicated that the two-nucleon density distribution, which gives the probability of finding a pair of nucleons as a function of the distance between the nucleons in the spin S=1, isospin T-0 states has interesting short-range structures. In the spin-projection M=0 state, the two-nucleon equidensity surfaces have toridal shape, while those in M=±1 states have dumbbell shapes related to the tori. These extremely small structures have a size of ~1 fm or 10^-15 meters. There is experimental evidence for the existence of such structures in nuclei, and more complex structures made from these are also predicted. Professor Pandharipande's team proposes to explore new methods to measure properties of these structures using modern electron accelerators. They obviously contain important information about nuclear forces which are not yet well understood. The team will also attempt to understand the relation between these structures and the forces between quarks, the most elementary constituents of nucleons and, therefore, also of nuclei.