Quark model and the nucleon-nucleon interaction

Abstract

The short and the long range part of the nucleon-nucleon interaction for the 3S and 1S partial waves are discussed starting from the quark model. It is shown that the use of the Born-Oppenheimer approximation for the calculation of the nucleon-nucleon interaction is not sufficient. At short distances quark and gluon exchange describes the interaction. Nonlocalities of NN force and of the reduced nucleon-nucleon mass have to be taken into account. It is shown that at short distances the spatial [42] symmetry of the six quarks is very essential for the understanding of the short range repulsion. At large distances meson exchange is used to describe the interaction. To guarantee asymptotic freedom, the mesons are not allowed to couple to the quarks inside the bag. This is taken care of by assuming a r dependent coupling constant g πqq (r) = C π r 3 for the π and σ meson exchange. The two parameters are adjusted to the known meson nucleon coupling constants at zero momentum transfer. The parameters of the model are adjusted to the nucleon and Δ mass, to the root mean square radius of the proton including the π-meson cloud, to the pion-nucleon and the σ-nucleon coupling constants and to the σ mass m σ =520 MeV. The Resonating Group Method is used to solve the nucleon-nucleon scattering problem and to calculate the 3S and 1S phase shifts. They agree surprisingly well with the data.