Magnetic HexadecapoleγTransitions and Neutrino-Nuclear Responses in Medium-Heavy Nuclei

Lotta Jokiniemi,Hiroyasu Ejiri,Jouni Suhonen

doi:10.1155/2016/8417598

Lotta Jokiniemi, Hiroyasu Ejiri + Show 1 more

Open Access

https://doi.org/10.1155/2016/8417598

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Abstract

Neutrino-nuclear responses in the form of squares of nuclear matrix elements, NMEs, are crucial for studies of neutrino-induced processes in nuclei. In this work we investigate magnetic hexadecapole (M4) NMEs in medium-heavy nuclei. The experimentally derived NMEs,MEXP(M4), deduced from observed M4γtransition half-lives are compared with the single-quasiparticle (QP) NMEs,MQP(M4), and the microscopic quasiparticle-phonon model (MQPM) NMEsMMQPM(M4). The experimentally derived M4 NMEs are found to be reduced by a coefficientk≈0.29with respect toMQP(M4) and byk≈0.33with respect toMMQPM(M4). The M4 NMEs are reduced a little by the quasiparticle-phonon correlations of the MQPM wave functions but mainly by other nucleonic and nonnucleonic correlations which are not explicitly included in the MQPM. The found reduction rates are of the same order of magnitude as those for magnetic quadrupoleγtransitions and Gamow-Teller (GT) and spin-dipole (SD)βtransitions. The impacts of the found reduction coefficients on the magnitudes of the NMEs involved in astroneutrino interactions and neutrinoless double beta decays are discussed.

Highlights

Neutrino interactions in nuclei are studied, for example, by investigating scatterings of astroneutrinos on nuclei and by the attempts to record the neutrinoless double beta (0]ββ) decays
The experimentally derived nuclear matrix elements (NMEs), MEXP(M4), deduced from observed M4 γ transition half-lives are compared with the single-quasiparticle (QP) NMEs, MQP(M4), and the microscopic quasiparticle-phonon model (MQPM) NMEs MMQPM(M4)
The neutrino-nuclear responses can be condensed in the squares of nuclear matrix elements (NMEs) and it is necessary to study through them the neutrino properties and astroneutrino reactions that are of interest to particle physics and astrophysics, as discussed in review articles [1,2,3,4] and references therein

Summary

Introduction

Neutrino interactions in nuclei are studied, for example, by investigating scatterings of astroneutrinos on nuclei and by the attempts to record the neutrinoless double beta (0]ββ) decays. The present work aims at investigating the magnetic hexadecapole (M4) γ NMEs, Mγ(M4), in medium-heavy nuclei to study higher-multipole axial-vector NMEs associated with higher-energy components of astroneutrino reactions and 0]ββ decays Such components are shown to be important for, for example, the 0]ββ decays [5]. Axial-vector CC resonances of GT(1+) and SD(2−) NMEs for allowed and first-forbidden β transitions are shown to be reduced much in comparison with the quasiparticle (QP) and pnQRPA (proton-neutron quasiparticle random-phase approximation) NMEs [6,7,8,9,10] due to spin-isospin (στ) nucleonic and nonnucleonic correlations and nuclear-medium effects These studies show that exact theoretical evaluations for the astroneutrino and 0]ββ NMEs, including possible renormalization of the axialvector coupling constant gA, are hard. We discuss mainly the M4 γ transitions in the present report with the aim of helping evaluate/confirm, for example, the 0]ββ NMEs concerning their higher-multipole aspects

Experimental M4 NMEs

Quasiparticle M4 NMEs

Microscopic Quasiparticle-Phonon Model for M4 NMEs

Reduction of the Axial-Vector NMEs

Findings

Discussion and Conclusions