Abstract

Neutrinoless double beta decay (DBD) is a useful probe to study neutrino properties such as the Majorana nature, the absolute neutrino mass, the CP phase and the others, which are beyond the standard model. The nuclear matrix element (NME) for DBD is crucial to extract the neutrino properties from the experimental transition rate. The neutrino-mass sensitivity, i.e., the minimum neutrino-mass to be measured by the DBD experiment, is very sensitive to the DBD NME. Actually, the NME is one of the key elements for designing the DBD experiment. Theoretical evaluation for the DBD NME, however, is very hard. Recently experimental studies of charge-exchange nuclear and leptonic reactions have shown to be used to get single-β NMEs associated with the DBD NME. Critical discussions are made on the neutrino-mass sensitivity and the NME for the DBD neutrino-mass study and on the experimental studies of the single-β NMEs and nuclear structures associated with DBD NMEs.

Highlights

  • Neutrinoless double beta decay (DBD), which violates the lepton-number (L) conservation law by ∆L = 2, is beyond the standard electro-weak model

  • Critical discussions are made on the neutrino-mass sensitivity and the nuclear matrix element (NME) for the DBD neutrino-mass study and on the experimental studies of the single-β NMEs and nuclear structures associated with DBD NMEs

  • Extensive experimental and theoretical studies of the DBDs are under progress to study the neutrino masses in inverted mass-hierarchy (IH) and normal mass-hierarchy (NH)

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Summary

Introduction

The DBD rate is proportional to the square of the effective neutrino mass me f f , which depends on the CP phases and the mass hierarchy. The DBD neutrino-mass sensitivity, which is defined as the minimum neutrino mass to be measured by the DBD experiment, is inversely proportional to the NME M0ν. The present report aims to discuss briefly the neutrino-mass sensitivity and the NME for the DBD experiment to access the neutrino masses of the current interest and the experimental ways to study single-β NMEs and nuclear structures associated with the DBD NME to help the theoretical evaluations for the DBD NME.

Neutrinoless DBD and Effective Neutrino Mass
DBD Neutrino-Mass Sensitivity and DBD Nuclear Matrix Element
Experimental Approaches to DBD NMEs
Experimental Studies of Two-Neutrino DBD NMEs
Nuclear Charge-Exchange Reactions
Photo-Nuclear Reactions
Quenching Coefficient for Weak Coupling and DBD NME
Findings
Concluding Remarks and Discussions
Full Text
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