Contribution of tensor forces to formation of Gamow-Teller Resonance and its overtone in closed-shell parent nuclei

Oct 13, 2020, 6:35 PM
1h
Online

Online

Poster report Section 1. Experimental and theoretical studies of the properties of atomic nuclei. Poster session 1 (part 1)

Speaker

Georgy Kolomiytsev (National Research Nuclear University MEPhI)

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).

  1. G.V. Kolomiytsev, M.G. Urin, Yad. Fiz. 83, 119 (2020).
  2. A.P. Severyukhin and H. Sagawa, Prog. Theor. Exp. Phys. 103D03 (2013).
  3. M.G. Urin, “Relaxation of nuclear excitations”. Moscow, Energoatomizdat, 1991 (in Russian).

Primary author

Dr Sergey Igashov (The Federal State Unitary Enterprise Dukhov Automatics Research Institute (VNIIA))

Co-authors

Georgy Kolomiytsev (National Research Nuclear University MEPhI) Michael Urin (National Research Nuclear University "MEPhI")

Presentation materials