Bochum 1998 – scientific programme

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HK: Hadronen und Kerne

HK 30: Nuclear Forces II, Theory

HK 30.2: Group Report

Tuesday, March 17, 1998, 14:30–15:00, F

Consistent use of the solitary boson exchange potential for πN and NN scattering — •L. Jäde and H.V. von Geramb — Theoretische Kernphysik, Universität Hamburg

Using the solitary boson exchange potential, OSBEP, we were able to describe very well the NN data below pion threshold without the use of phenomenologic form factors. Here, we extend and apply this model to πN scattering. These two systems deserve attention since conventional boson exchange models lack a consistent description with a common set of parameters and, in particular, form factors. Standard boson exchange models require a pion form factor which is soft for πN (Λ_π ≤ 1 GeV) and hard for NN scattering (Λ_π > 1 GeV). The solitary boson exchange potential regularizes the amplitudes in a different way and, as this analysis shows, the inconsistencies disappear. Furthermore, we maintain the empirical scaling relation for the meson nonlinearities, which was first seen in the NN analysis, for the combined NN and πN OSBEP model. We show results for np and pp observables as well as the underlying partial wave phase shifts in comparison with other models and experimental data taken from SAID. In addition, we compare the OSBEP πN phase shifts with the latest experimental results. The agreement with data is consistently good for NN and πN. Finally, we address the problem of the low–energy theorems of πN scattering. We show that the scattering lengths as a function of pion mass do not contradict the Weinberg–Tomozawa relations.