Microscopic Interacting Boson Model Research Articles

High-precision Q-value measurement and nuclear matrix element calculations for the double-beta decay of ^{98}Mo

The ^{98}Mo double-beta decay Q-value has been measured, and the corresponding nuclear matrix elements of neutrinoless double-beta (0nu beta beta ) decay and the standard two-neutrino double-beta (2nu beta beta ) decay have been provided by nuclear theory. The double-beta decay Q-value has been determined as Q_{beta beta }=113.668(68) keV using the JYFLTRAP Penning trap mass spectrometer. It is in agreement with the literature value, Q_{beta beta }=109(6) keV, but almost 90 times more precise. Based on the measured Q-value, precise phase-space factors for 2nu beta beta decay and 0nu beta beta decay, needed in the half-life predictions, have been calculated. Furthermore, the involved nuclear matrix elements have been computed in the proton–neutron quasiparticle random-phase approximation (pnQRPA) and the microscopic interacting boson model (IBM-2) frameworks. Finally, predictions for the 2nu beta beta decay are given, suggesting a much longer half-life than for the currently observed cases.

Comparison of Microscopic Interacting Boson Model and Quasiparticle Random Phase Approximation 0νββ Decay Nuclear Matrix Elements

The fundamental nature of the neutrino is presently a subject of great interest. A way to access the absolute mass scale and the fundamental nature of the neutrino is to utilize the atomic nuclei through their rare decays, the neutrinoless double beta (0νββ) decay in particular. The experimentally measurable observable is the half-life of the decay, which can be factorized to consist of phase space factor, axial vector coupling constant, nuclear matrix element, and function containing physics beyond the standard model. Thus reliable description of nuclear matrix element is of crucial importance in order to extract information governed by the function containing physics beyond the standard model, neutrino mass parameter in particular. Comparison of double beta decay nuclear matrix elements obtained using microscopic interacting boson model (IBM-2) and quasiparticle random phase approximation (QRPA) has revealed close correspondence, even though the assumptions in these two models are rather different. The origin of this compatibility is not yet clear, and thorough investigation of decomposed matrix elements in terms of different contributions arising from induced currents and the finite nucleon size is expected to contribute to more accurate values for the double beta decay nuclear matrix elements. Such comparison is performed using detailed calculations on both models and obtained results are then discussed together with recent experimental results.

Role of Single-Particle Energies in Microscopic Interacting Boson Model Double Beta Decay Calculations

Single-particle level energies form a significant input in nuclear physics calculations where single-particle degrees of freedom are taken into account, including microscopic interacting boson model investigations. The single-particle energies may be treated as input parameters that are fitted to reach an optimal fit to the data. Alternatively, they can be calculated using a mean field potential, or they can be extracted from available experimental data, as is done in the current study. The role of single-particle level energies in the microscopic interacting boson model calculations is discussed with special emphasis on recent double beta decay calculations.

Double beta decay and the quest for Majorana neutrinos

The observation of neutrinoless double beta (0νββ) decay remains crucial for understanding lepton number violation. The inverse half-life for 0νββ-decay is given by the product of a phase space factor (PSF), a nuclear matrix element (NME), which both rely on theoretical description, and a function f containing the physics beyond the standard model. Phase space factors and nuclear matrix elements have been evaluated, or are under evaluation, systematically for all processes of interest. The nuclear matrix elements have been calculated within the framework of the microscopic interacting boson model (IBM-2), and phase space factors have been evaluated using exact Dirac electron wave functions. The current situation is then discussed by combining the theoretical results with experimental limits on the half-life of neutrinoless double beta decay. The extracted limits on the average light neutrino mass are addressed, complemented with a discussion of other possible 0νββ-decay mechanisms and scenarios.

SU (3) Symmetry of Even-Even 150, 152Ce Isotopes in the Microscopic Interacting Boson Model (IBM-1)

SU (3) Symmetry of Even-Even ^{150, 152}Ce Isotopes in the Microscopic Interacting Boson Model (IBM-1)

Two-nucleon transfer and Double Charge Exchange reactions

In this contribution we present a study of a direct and sequential two-nucleon transfer within the microscopic Interacting Boson Model (IBM-2) and Interacting Boson- Fermion Model (IBFM), respectively. We present our preliminary results for heavy-ion double-charge-exchange40Ca(18O,18Ne)40ArG.S. differential cross section too.

Single Particle Levels and ββ-Decay Matrix Elements in The Interacting Boson Model

Recently a new method to calculate the occupancies of single particle levels in atomic nuclei was developed in the context of the microscopic interacting boson model, in which neutron and proton degrees of freedom are treated explicitly (IBM-2). The energies of the single particle levels constitute a very important input for the calculation of the occupancies in this method, and further they play important role in the calculation of double beta decay nuclear matrix elements. Here we discuss how the 0νββ, 0νhββ, and 2νββ-decay nuclear matrix elements (NMEs) are affected when the energies of single particle levels are changed.

Occupation probabilities of single particle levels using the microscopic interacting boson model: Application to some nuclei of interest in neutrinoless double-βdecay

We have developed a new method to calculate the occupancies of single particle levels in atomic nuclei. This method has been developed in the context of the microscopic interacting boson model, in which neutron and proton degrees of freedom are treated explicitly. The energies of the single particle levels constitute a very important input for the calculation of the occupancies in this method. In principle these energies can be considered as input parameters that can be fitted to reproduce the experimental occupancies. Instead of fitting, in this study we have extracted the single particle energies from experimental data on nuclei with a particle more or one particle less than a shell closure. We provide the sets of these single particle energies suitable for several major shells and apply our method to calculate the occupancies of several nuclei of interest in neutrinoless double-$\ensuremath{\beta}$ decay using these sets. Our results are compared with other theoretical calculations and experimental occupancies, when available.

Recent results in double beta decay

Nuclear matrix elements for 0νββ, 0νhββ, and 2νββ decay in the microscopic interacting boson model (IBM-2) with isospin restoration are given for all nuclei of interest from 48Ca to 238U.

Neutrinoless double-electron capture

Direct determination of the neutrino mass is at the present time one of the most important aims of experimental and theoretical research in nuclear and particle physics. A possible way of detection is through neutrinoless double-electron capture, $0\ensuremath{\nu}\mathrm{ECEC}$. This process can only occur when the energy of the initial state matches precisely that of the final state. We present here a calculation of prefactors (PFs) and nuclear matrix elements (NMEs) within the framework of the microscopic interacting boson model (IBM-2) for $^{124}\mathrm{Xe}$, $^{152}\mathrm{Gd}$, $^{156}\mathrm{Dy}$, $^{164}\mathrm{Er}$, and $^{180}\mathrm{W}$. From the PF and NME we calculate the expected half-lives and obtain results that are of the same order as those of $0\ensuremath{\nu}{\ensuremath{\beta}}^{+}{\ensuremath{\beta}}^{+}$ decay, but considerably longer than those of $0\ensuremath{\nu}{\ensuremath{\beta}}^{\ensuremath{-}}{\ensuremath{\beta}}^{\ensuremath{-}}$ decay.

Neutrinoless double-positron decay and positron-emitting electron capture in the interacting boson model

Neutrinoless double-$\ensuremath{\beta}$ decay is of fundamental importance for determining the neutrino mass. Although double electron decay is the most promising mode, in very recent years interest in double positron decay, positron emitting electron capture, and double electron capture has been renewed. We present here results of a calculation of nuclear matrix elements for neutrinoless double-${\ensuremath{\beta}}^{+}$ decay and positron emitting electron capture within the framework of the microscopic interacting boson model (IBM-2) for ${}^{58}$Ni, ${}^{64}$Zn, ${}^{78}$Kr, ${}^{96}$Ru, ${}^{106}$Cd, ${}^{124}$Xe, ${}^{130}$Ba, and ${}^{136}$Ce decay. By combining these with a calculation of phase space factors we calculate expected half-lives.

A compilation of [formula omitted] nuclear matrix elements in the interacting boson model

Nuclear matrix elements for 0νββ and 0νhββ decay in the microscopic interacting boson model (IBM-2) are given for all nuclei of interest from 48Ca to 238U.

Nuclear matrix elements for double-βdecay

Background: Direct determination of the neutrino mass through double-$\beta$ decay is at the present time one of the most important areas of experimental and theoretical research in nuclear and particle physics. Purpose: We calculate nuclear matrix elements for the extraction of the average neutrino mass in neutrinoless double-$\beta$ decay. Methods: The microscopic interacting boson model (IBM-2) is used. Results: Nuclear matrix elements in the closure approximation are calculated for $^{48}$Ca, $^{76}$Ge, $^{82}$Se, $^{96}$Zr, $^{100}$Mo, $^{110}$Pd, $^{116}$Cd, $^{124}$Sn, $^{128}$Te, $^{130}$Te, $^{148}$Nd, $^{150}$Nd, $^{154}$Sm, $^{160}$Gd, and $^{198}$Pt decay. Conclusions: Realistic predictions for the expected half-lives in neutrinoless double-$\beta$ decay with light and heavy neutrino exchange in terms of neutrino masses are made and limits are set from current experiments.

A probable explanation on nuclear shape phase transition SU(3)–U(5)–SU(3) of the yrast-band structure in 182Os nucleus by potential energy surface

Nuclear structure phase transitions SU(3)–U(5)–SU(3) of the yrast-band structure in 182Os nucleus are successfully described, based on the association of microscopic interacting Boson model (IBM) with the γ-ray energy on spin curves (E-GOS). It is very abstract because of lack of concrete facts. A probable explanation of these one after the other phase transitions are geometrically given, with a functional relation of microscopic parameters in microscopic sdIBM-Fmax approach and potential energy surface in Bohr collective model. It is expounded that at high angular momentum, in a well-deformed nucleus, a probable way to the γ-vibrational energy can become lower than the rotational energy bcause there are a number of degeneracy states formed by quantum effect between the highter and lower excition states so as to achieve SU(3)–U(5) structue phase transition.

Limits on Neutrino Masses from Neutrinoless Double-βDecay

Neutrinoless double-β decay is of fundamental importance for the determining neutrino mass. By combining a calculation of nuclear matrix elements within the framework of the microscopic interacting boson model with an improved calculation of phase space factors, we set limits on the average light neutrino mass and on the average inverse heavy neutrino mass (flavor-violating parameter).

Neutrinoless double-βdecay in the microscopic interacting boson model

We present a formalism for calculating nuclear matrix elements of double-$\ensuremath{\beta}$ decay within the framework of the microscopic interacting boson model. We calculate Fermi, Gamow-Teller, and tensor matrix elements in the decay of Ge-Se-Mo-Te-Xe-Nd-Sm and compare our results with those of the shell-model (SM) and of the quasiparticle random-phase approximation (QRPA). Our results are in agreement with QRPA. We discuss simple features of the matrix elements and give a formula that allows one to estimate matrix elements in terms of the number of valence proton and neutron pairs.

Microscopic interacting boson model calculations for even-even 128–138Ce nuclei

In this study, we determined the most appropriate Hamiltonian that is needed for the present calculations of energy levels and B(E2) values of 128–138Ce nuclei which have a mass around A≅130 using the interacting boson model (IBM). Using the best-fitted values of parameters in the Hamiltonian of the IBM-2, we have calculated energy levels and B(E2) values for a number of transitions in 128,130,132,134,136,138Ce. The results were compared with the previous experimental and theoretical (PTSM model) data and it was observed that they are in good agreement. Also some predictions of this model have better accuracy than those of PTSM model. It has turned out that the interacting boson approximation (IBA) is fairly reliable for calculating spectra in the entire set of 128,130,132,134,136,138Ce isotopes and the quality of the fits presented in this paper is acceptable.

Microscopic derivation of the interacting boson Hamiltonian from a phenomenological interaction

A microscopic interacting boson model calculation is performed for Ba isotopes. The boson interactions are constructed by applying the Otsuka–Arima–Iachello mapping procedure to the phenomenological interactions given in previous systematic studies for A ∼ 130 nuclei. The theoretical energy levels in the IBM are found to be in good agreement with those of the pair-truncated shell model.

Shape transitions in even Mo and Sm isotopes: Study in a new microscopic interacting boson model scheme

A simple dynamic procedure, based on the deformed Hartree-Fock solution of a nucleus, is presented to construct the IBM operators in microscopic basis. The parameters of these operators are evaluated by establishing a Marumori mapping from the truncated shell model space onto the boson space. The transitions from spherical to axial-rotor shape observed in the low-lying levels ofeven96–108Mo and146–154Sm isotopes are reproduced qualitatively by applying this procedure with a fixed set of fermion input parameters to each chain. Variation of a few parameters in fermion space leads to quantitative agreement.

Application of a microscopic interacting boson model to single-closed-shell nuclei

The microscopic treatment of an extended IBM including the pairing vibrational modes is applied to single-closed-shell nuclei with N = 50 or Z = 50. The low-lying spectra in the N = 50 isotones are well described in terms of the quadrupole phonon and the pairing vibration. The Sn isotopes roughly resemble the N = 50 isotones. The behavior of the 0 2 +, 0 3 + and 2 1 + levels can be explained fairly well by the present model. Introduction of the pairing-vibrational modes into the IBM is essential for describing the single-closed-shell nuclei.