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Theory Center Research Highlights

Few-Body Nuclear Physics and the Nucleon-Nucleon Force

"Covariant spectator theory of np scattering: Phase shifts and covariant one-boson-exchange potentials obtained from high precision fits to data below 350 MeV"
F. Gross and A. Stadler
Phys. Lett. B 657, 176 (2007) & arXiv:0802.1552 [nucl-th]

A major goal of nuclear physics and the JLab scientific program is to obtain an understanding of the nuclear force. Part of this effort involves finding a potential that will give a high precision fit to the NN data below 350 MeV. The well known Nijmegen, Argonne, and Bonn (Idaho) potentials are to some extent based on one boson exchange (OBE), but in order to achieve an essentially perfect fit to the scattering data they all had to abandon OBE and lose the easy extension to electromagnetic processes provided by this simple mechanism. Recently, using the covariant spectator theory, a covariant OBE potential has been found that gives an excellent high precision fit to the NN scattering data (see the table). Furthermore, this potential has fewer adjustable parameters than previous high-precision potentials, and also reproduces the experimental triton binding energy without additional irreducible three-nucleon forces. This simple new force is now being used to study few-body measurements at JLab.

"Few-nucleon forces and systems in chiral effective field theory"
E. Epelbaum
Prog. Part. Nucl. Phys. 57, 654 (2006)

We outline the structure of the nuclear force in the framework of chiral effective field theory of QCD and review recent applications to processes involving few nucleons.

"Modern theories of low-energy astrophysical reactions"
L.E. Marcucci, K.M. Nollett, R. Schiavilla, R.B. Wiringa
Nucl. Phys. A777, 111 (2006)

We summarize recent ab initio studies of low-energy electroweak reactions of astrophysical interest, relevant for both big bang nucleosynthesis and solar neutrino production. The calculational methods include direct integration for np radiative and pp weak capture, correlated hyperspherical harmonics for reactions of A=3,4 nuclei, and variational Monte Carlo for A=6,7 nuclei. Realistic nucleon-nucleon and three-nucleon interactions and consistent current operators are used as input.