Speaker
Description
A mean-field and interaction in the particle-hole (p-h) channel are the input quantities for any RPA-based approach to describing Gamow-Teller Resonance and its overtone – Isovector Giant Spin-Monopole Resonance in the $\beta^{(−)}$ -channel (GTR and IVGSMR$^{(−)})$ , respectively). The recent example of such an approach is given in Ref. [1], where main properties of mentioned resonances in $^{208}$Bi are described within the continuum-RPA-based semimicroscopic p-h dispersive optical model. A realistic partially self-consistent phenomenological mean field and Landau-Migdal p-h interaction have been used in this study. Provided that dimensionless strength $g'$ of the spin-isospin part of the mentioned interaction is adjusted to reproduce in calculations of the GT strength function the observable GTR energy, the calculated IVGSMR$^{(−)})$ energy is found to be less (on about 3 MeV) than respective experimental value. In the present study, we attempt to resolve this puzzle by taking into account tensor forces, which lead to mixing $1^+$ spin-monopole and spin-quadrupole excitations. In applying to describing GT strength distribution, tensor forces have been considered in Ref. [2]. Mentioned mixing takes place due to both the spin-orbit term in a mean field (so-called nonsymmetric or non-diagonal approximation in RPA-based approaches employing central forces [3]) and non-central (tensor) forces. Using the mentioned
continuum-RPA-based analysis of Ref. [1] as a starting point, we resolved the above-described puzzle related to evaluation of the IVGSMR$^{(−)})$ energy by taking tensor forces into account. As expected, the strength parameter of the spin-isospin part of non-central forces $g_T'$ is found to be less than the Landau-Migdal parameter $g'$.
This work was partially supported by the Russian Foundation of Basic Research (grant No. 19-02-00660).
- G.V. Kolomiytsev, M.G. Urin, Yad. Fiz. 83, 119 (2020).
- A.P. Severyukhin and H. Sagawa, Prog. Theor. Exp. Phys. 103D03 (2013).
- M.G. Urin, “Relaxation of nuclear excitations”. Moscow, Energoatomizdat, 1991 (in Russian).
