In this work,the characteristics of 2νββ decays for six nuclei(36Ar,46Ca,48Ca,50Cr,70Zn,and 136Xe)in a mass range from A=36 to A=136 are studied within the nuclear shell model(NSM)framework.Calculations are present...In this work,the characteristics of 2νββ decays for six nuclei(36Ar,46Ca,48Ca,50Cr,70Zn,and 136Xe)in a mass range from A=36 to A=136 are studied within the nuclear shell model(NSM)framework.Calculations are presented for the half-lives,nuclear matrix elements(NMEs),phase space factors(G2ν),and convergence of the NMEs.The theoretical results agree well with the experimental data.In addition,we predict the half-lives of 2νββ decays for four nuclei.We focus on the convergence of the NMEs by analyzing the number of contributing intermediate 1+states(NC)for the nuclei of interest.We assume that NC is safely determined when the accumulated NMEs saturate 99.7%of the final calculated magnitude.From the calculations of the involved nuclei,we discover a connection between NC and the total number of intermediate 1+states(NT).According to the least squares fit,we conclude that the correlation is NC=(10.8±1.2)×N(0.29±0.02)T.展开更多
Nuclear matrix elements(NME) and phase space factors(PSF) entering the half-life formulas of the double-beta decay(DBD) process are two key quantities whose accurate computation still represents a challenge. In this s...Nuclear matrix elements(NME) and phase space factors(PSF) entering the half-life formulas of the double-beta decay(DBD) process are two key quantities whose accurate computation still represents a challenge. In this study, we propose a new approach of calculating these, namely the direct computation of their product as an unique formula. This procedure allows a more coherent treatment of the nuclear approximations and input parameters appearing in both quantities and avoids possible confusion in the interpretation of DBD data due to different individual expressions adopted for PSF and NME(and consequently their reporting in different units) by different authors. Our calculations are performed for both two neutrino(2 vββ) and neutrinoless(0 vββ) decay modes, for five nuclei of the most experimental interest. Further, using the most recent experimental limits for 0νββ decay half-lives,we provide new constraints on the light mass neutrino parameter. Finally, by separating the factor representing the axial-vector constant to the forth power in the half-life formulas, we advance suggestions on how to reduce the errors introduced in the calculation by the uncertain value of this constant, exploiting the DBD data obtained from different isotopes and/or decay modes.展开更多
We present analytical method to calculate single particle matrix elements used in atomic and nuclear physics. We show seven different formulas of matrix elements of the operator f(r)d_r^m where f(r) = r~μ, r~μjJ(qr)...We present analytical method to calculate single particle matrix elements used in atomic and nuclear physics. We show seven different formulas of matrix elements of the operator f(r)d_r^m where f(r) = r~μ, r~μjJ(qr), V(r)corresponding to the Gaussian and the Yukawa potentials used in nuclear shell models and nuclear structure. In addition,we take into account a general integral formula of the matrix element 〈 n′ l′|f(r) d_r^(m) |n l〉 that covers all seven matrix elements obtained analytically.展开更多
Using partially restored isospin symmetry,we calculate the nuclear matrix elements for a special decay mode of a two-neutrino double beta decay–the decay to the first 2+excited states.Employing the realistic CD–Bonn...Using partially restored isospin symmetry,we calculate the nuclear matrix elements for a special decay mode of a two-neutrino double beta decay–the decay to the first 2+excited states.Employing the realistic CD–Bonn nuclear force,we analyze the dependence of the nuclear matrix elements on the isovector and isoscalar parts of proton–neutron particle–particle interactions.The dependence on the different nuclear matrix elements is observed,and the results are explained.We also provide the phase space factors using numerical electron wavefunctions and properly chosen excitation energies.Finally,we present our results for the half-lives of this decay mode for different nuclei.展开更多
基金Supported by National Natural Science Foundation of China(11647086,11647085)Shanxi Province Science Foundation for Youths(201901D211252)+1 种基金Scientific and Technological Innovation Programs of Higher Education Institutions in Shanxi(2019L0554,2019L0505)the Natural Science Research Fund of North University of China(XJJ201811)。
文摘In this work,the characteristics of 2νββ decays for six nuclei(36Ar,46Ca,48Ca,50Cr,70Zn,and 136Xe)in a mass range from A=36 to A=136 are studied within the nuclear shell model(NSM)framework.Calculations are presented for the half-lives,nuclear matrix elements(NMEs),phase space factors(G2ν),and convergence of the NMEs.The theoretical results agree well with the experimental data.In addition,we predict the half-lives of 2νββ decays for four nuclei.We focus on the convergence of the NMEs by analyzing the number of contributing intermediate 1+states(NC)for the nuclei of interest.We assume that NC is safely determined when the accumulated NMEs saturate 99.7%of the final calculated magnitude.From the calculations of the involved nuclei,we discover a connection between NC and the total number of intermediate 1+states(NT).According to the least squares fit,we conclude that the correlation is NC=(10.8±1.2)×N(0.29±0.02)T.
基金Supported by Ministry of Research and Innovation through UEFISCDI,project PCE-2016-0078,contract 198/2017
文摘Nuclear matrix elements(NME) and phase space factors(PSF) entering the half-life formulas of the double-beta decay(DBD) process are two key quantities whose accurate computation still represents a challenge. In this study, we propose a new approach of calculating these, namely the direct computation of their product as an unique formula. This procedure allows a more coherent treatment of the nuclear approximations and input parameters appearing in both quantities and avoids possible confusion in the interpretation of DBD data due to different individual expressions adopted for PSF and NME(and consequently their reporting in different units) by different authors. Our calculations are performed for both two neutrino(2 vββ) and neutrinoless(0 vββ) decay modes, for five nuclei of the most experimental interest. Further, using the most recent experimental limits for 0νββ decay half-lives,we provide new constraints on the light mass neutrino parameter. Finally, by separating the factor representing the axial-vector constant to the forth power in the half-life formulas, we advance suggestions on how to reduce the errors introduced in the calculation by the uncertain value of this constant, exploiting the DBD data obtained from different isotopes and/or decay modes.
文摘We present analytical method to calculate single particle matrix elements used in atomic and nuclear physics. We show seven different formulas of matrix elements of the operator f(r)d_r^m where f(r) = r~μ, r~μjJ(qr), V(r)corresponding to the Gaussian and the Yukawa potentials used in nuclear shell models and nuclear structure. In addition,we take into account a general integral formula of the matrix element 〈 n′ l′|f(r) d_r^(m) |n l〉 that covers all seven matrix elements obtained analytically.
基金Supported by National Natural Science Foundation of China(11505078,1164730)“Light of West China”Program and key research program(XDPB09-2)from Chinese Academy of Sciences。
文摘Using partially restored isospin symmetry,we calculate the nuclear matrix elements for a special decay mode of a two-neutrino double beta decay–the decay to the first 2+excited states.Employing the realistic CD–Bonn nuclear force,we analyze the dependence of the nuclear matrix elements on the isovector and isoscalar parts of proton–neutron particle–particle interactions.The dependence on the different nuclear matrix elements is observed,and the results are explained.We also provide the phase space factors using numerical electron wavefunctions and properly chosen excitation energies.Finally,we present our results for the half-lives of this decay mode for different nuclei.