Forbidden transitions in nuclear weak processes relevant to neutrino detection, nucleosynthesis and evolution of stars

Toshio Suzuki,Satoshi Chiba,Koh Takahashi,Takashi Yoshida,Hideyuki Umeda,Ken’ichi Nomoto

doi:10.1051/epjconf/201922301063

Abstract

The distribution of the spin-dipole strengths in 16O and neutrino-induced reactions on 16O areinvestigated by shell-model calculations with new shell-model Hamiltonians. Chargedcurrent and neutral-current reactioncross sections are valuated in various particle and γ emission channels as well as the total ones at neutrinoenergies up to Eν≈ 100 MeV. Effects of multiparticle emission channels, especially the αp emission channels, on nucleosynthesis of 11B and 11C in core-collapse supernova explosions are investigated. The MSW neutrino oscillation effects oncharged-current reaction cross sections are investigated for future supernova burst. Electron capture rates for a forbidden transition 20Ne(Og.s.+) → 20F(2g.s.+) in stellar environments are evaluated by the multipole expansion method with the use of shell model Hamiltonians, and compared with those obtained by a prescription that treats the transition as an allowed GamowTeller (GT) transition. Different electron energy dependence of the transition strengths between the two methods is found to lead to sizable differences in the weak rates of the two methods.

Highlights

Roles of Gamow-Teller (GT) transitions in nuclear weak rates at stellar environments have been investigated in various astrophysical processes
Forbidden transitions in 16O and 20Ne are studied by shell-model calculations with the use of new shellmodel Hamiltonians
Total and partial ν-induced reactions on 16O in various channels including multiparticle emissions are obtained with the SFO-tls, which can reproduce low-lying spin-dipole states in 16O

Summary

Introduction

Roles of Gamow-Teller (GT) transitions in nuclear weak rates at stellar environments have been investigated in various astrophysical processes. Electron-capture and β-decay rates in sd-shell nuclei have been updated, and applied to nuclear URCA processes in O-Ne-Mg core of stars with M=8-10M☉ [13]. We focus on forbidden transitions in 16O and 20Ne. We discuss spin-dipole strengths in 16O and ν-induced reactions on 16O in Sect. Spin-dipole strength in 16O ν-induced reactions on 12C was studied with a shellmodel Hamiltonian, SFO [15], which can reproduce the GT strength in 12C and magnetic moments of p-shell nuclei systematically. Charged- and neutral-current ν-nucleus reaction cross sections on 16O are evaluated by shell-model calculations with the SFO-tls [18]. The cross sections for SFO-tls are enhanced compared with those of SFO, and found to be close to those of the CRPA except at Eν < 30 MeV. Enhancement of expected event numbers for supernovae at 10 kpsc away from the earth is predicted for the e ( e ) -induced reaction in case of normal (inverted) hierachy [23]

Evolution of O-Ne-Mg cores in stars

Summary