Effects of a Skyrme-type tensor force on the spin-isospin excitations

C.L Bai,F.R Xu,H Sagawa,X.Z Zhang,H.Q Zhang,G Colò

doi:10.1051/epjconf/20146602004

Abstract

The effects of the tensor force on the charge-exchange Gamow-Teller (GT) and spin-dipole (SD) states are studied by using the self-consistent Hartree-Fock plus Random Phase Approximation (HF+RPA) approach based on Skyrme zero-range forces. We have found, not surprisingly, thatthe tensor force has a large effect on the GT strength. In the case of the SD excitations, the tensor force produces a softening of the 1 − states, but a hardening of 0 − and 2 − states: these effects improve the agreement with the experi- mental findings. We have also studied how to constrain the magnitude of the tensor terms of the Skyrme interaction by using the empirical information on the collective GT and SD excited states in 90 Zr and 208 Pb.

Highlights

An effective zero-range tensor interaction has been proposed by Skyrme, at the same time as the wellknown central and spin-orbit terms, in the 1950s [1]
Since the tensor force affects the spin-orbit splittings of finite nuclei, another possibility is to add it to some existing Skyrme parameter set and to fit the tensor terms so to reproduce at best the evolution of single-particle states along isotopic or isotonic chains [4, 5]
The most prominent effect induced by the tensor correlations is that the main GT− peaks are shifted downwards by about 2 MeV; as a result, their energies are somewhat lower than the experimental result and this points to the necessity of refitting the Skyrme parameters after adding tensor terms

Summary

Introduction

An effective zero-range tensor interaction has been proposed by Skyrme, at the same time as the wellknown central and spin-orbit terms, in the 1950s [1]. Since the tensor force affects the spin-orbit splittings of finite nuclei, another possibility is to add it to some existing Skyrme parameter set and to fit the tensor terms so to reproduce at best the evolution of single-particle states along isotopic or isotonic chains [4, 5]. Another plausible way to obtain an effective interaction with tensor terms is to implement a full variational procedure and fit the tensor and the central terms of the Skyrme interaction on equal footing [6].

Pb GT

Quantitative Constraints to the Tensor Force

Summary