High-lying excited states in Gamow Teller strength and their roles in neutrino reactions

Abstract

The Gamow Teller (GT) transition strengths deduced from charge exchange reactions (CEXRs) are very helpful for understanding the nuclear reaction induced by neutrinos, in particular, by the solar neutrino. For further study of supernovae (SNe) neutrinos in the cosmos, one needs to study high-lying GT states around a few tens of MeV region as well as other multipole transitions because of the high energy tail in the neutrino spectra emitted from the neutrino sphere. In this report, we address the importance of the high-lying GT excited states, whose data now become available from various CEXR experiments. For example, GT(± strengths up to 70MeV are successfully extracted by ⁹⁰Zr(n, p) and ⁹⁰Zr(p, n) reactions. Our discussions are extended to investigate roles of the high-lying states beyond a few low-lying states known in the old experiment on the reaction induced by SNe neutrinos particularly on ⁴⁰Ar target. The nucleus was originally exploited to identify the solar neutrino emitted from ⁸B produced in the pp-chains on the Sun, and now lots of applications for more energetic neutrino detection are under progress. The expected large difference between the cross-sections of $\nu_{e}^{}$ and $\bar{{\nu}}_{e}^{}$ reactions on ⁴⁰Ar , whose differences were anticipated because of the large Q-value in the $\bar{{\nu}}_{e}^{}$ reaction, is significantly diminished compared to previous results. Our calculations are carried out by the Quasi-particle Random Phase Approximation (QRPA), which takes the neutron-proton pairing into account to the standard proton-neutron QRPA (pnQRPA) where only proton-proton and neutron-neutron pairing correlations are considered.