Roles of High-lying Excited States on Neutrino Reactions and the Gamow Teller strength for $^{40}$Ar

TL;DR

This paper investigates how high-lying excited states in $^{40}$Ar influence neutrino reactions relevant for detecting solar and supernova neutrinos, showing that their inclusion reduces the expected cross section differences.

Contribution

The study incorporates high-lying excited states up to a few tens of MeV in QRPA calculations, providing a more accurate understanding of neutrino interactions with $^{40}$Ar.

Findings

High-lying states significantly affect neutrino reaction cross sections.

The difference between $ u_e$ and $ar{ u}_e$ reactions is reduced to about a factor of 2.

QRPA successfully models neutrino reactions and nuclear beta decay data.

Abstract

Neutrino reactions on $^{40}$Ar via charged and neutral currents for detecting solar and core collapsing supernovae (SNe) neutrinos and the Gamow Teller strength are calculated by considering the high-lying excited states up to a few tens of MeV region. The nucleus was originally exploited to identify the solar neutrino emitted from $^{8}$B produced in the pp-chains on the Sun. With the higher energy neutrinos emitted from the core collapsing SNe, contributions from higher multi-pole transitions including the spin dipole resonances (SDR) as well as the Gamow Teller (GT) and Fermi transitions are shown to be important ingredients for understanding reactions induced by the SNe as well as solar neutrinos. In this work, we focused on the role of high-lying excited states which are located beyond a few low-lying states known in the experiment. Expected large difference between the cross sections of $\nu_e$ and ${\bar \nu_e}$ reactions on $^{40}$Ar, which difference has been anticipated in previous calculations because of the large Q value in the ${\bar \nu}_e$ reaction, is significantly diminished. The reduction leads only to about 2 times difference between them. Our calculations are carried out by the Quasi-particle Random Phase Approximation (QRPA), which takes account of the neutron-proton pairing as well as proton-proton and neutron-neutron pairing correlations. They were successfully applied in the description of the nuclear beta decay and relevant neutrino reaction data on $^{12}$C and $^{56}$Fe, and the GT data on the $^{138}$La and $^{180}$Ta.