Microscopic Quasiparticle-phonon Model Research Articles

Neutral-current supernova neutrino-nucleus scattering off I127 and Cs133

A large number of the presently running neutrino and dark-matter experiments use thallium-doped cesium-iodide CsI[Tl] crystals, sodium-doped cesium-iodide CsI[Na] crystals, or thallium-doped sodium-iodide NaI[Tl] crystals. In the present paper we calculate elastic and inelastic cross sections for neutral-current supernova-neutrino scattering off $^{127}\mathrm{I}$ and $^{133}\mathrm{Cs}$, relevant for experiments using CsI[Tl], CsI[Na], or NaI[Tl] crystals. We study also the cross sections folded with two-parameter Fermi-Dirac distributions of the supernova-neutrino spectrum. The adopted nuclear-theory framework is the microscopic quasiparticle-phonon model, able to operate in large single-particle valence bases and use G-matrix based two-nucleon interactions with a phenomenological renormalization.

Low-lying electric dipole γ-continuum for the unstable 62,64Fe nuclei: Strength evolution with neutron number

The γ-ray emission from the nuclei 62,64Fe following Coulomb excitation at bombarding energy of 400-440 AMeV was measured with special focus on E1 transitions in the energy region 4-8 MeV. The unstable neutron-rich nuclei 62,64Fe were produced at the FAIR-GSI laboratories and selected with the FRS spectrometer. The γ decay was detected with AGATA. From the measured γ-ray spectra the summed E1 strength is extracted and compared to microscopic quasi-particle phonon model calculations. The trend of the E1 strength with increasing neutron number is found to be fairly well reproduced with calculations that assume a rather complex structure of the 1− states (three-phonon states) inducing a strong fragmentation of the E1 nuclear response below the neutron binding energy.

Charged-current neutrino-nucleus scattering off Xe isotopes

Xenon detectors are used in the search for dark matter and neutrinoless double-beta decay ($0\ensuremath{\nu}\ensuremath{\beta}\ensuremath{\beta})$. As the next-generation detectors reach masses in the ton scale, neutrinos from astrophysical sources are soon predicted to become background in such detectors. Theoretical predictions of neutrino scattering cross sections and information of nuclear structure effects therein are crucial in accounting for the background. We perform calculations for differential and total cross sections of charged-current neutrino scattering off the most abundant xenon isotopes. The nuclear-structure calculations are made in the proton-neutron quasiparticle random-phase approximation and the microscopic quasiparticle phonon model for even-mass and odd-mass nuclei, respectively. We compute total cross sections as a function of the neutrino energy, and also give estimates of total averaged cross sections for $^{8}\mathrm{B}$ solar neutrinos and supernova neutrinos using realistic energy distributions.

Neutral-Current Neutrino-Nucleus Scattering off Xe Isotopes

Large liquid xenon detectors aiming for dark matter direct detection will soon become viable tools also for investigating neutrino physics. Information on the effects of nuclear structure in neutrino-nucleus scattering can be important in distinguishing neutrino backgrounds in such detectors. We perform calculations for differential and total cross sections of neutral-current neutrino scattering off the most abundant xenon isotopes. The nuclear-structure calculations are made in the nuclear shell model for elastic scattering and also in the quasiparticle random-phase approximation (QRPA) and microscopic quasiparticle-phonon model (MQPM) for both elastic and inelastic scattering. Using suitable neutrino energy distributions, we compute estimates of total averaged cross sections for ​8B solar neutrinos and supernova neutrinos.

GA -driven shapes of electron spectra of forbidden β decays in the nuclear shell model

The evolution of the shape of the electron spectra of 16 forbidden ${\ensuremath{\beta}}^{\ensuremath{-}}$ decays as a function of ${g}_{\mathrm{A}}$ was studied using the nuclear shell model in appropriate single-particle model spaces with established, well-tested nuclear Hamiltonians. The $\ensuremath{\beta}$ spectra of $^{94}\mathrm{Nb}({6}^{+})\ensuremath{\rightarrow}\phantom{\rule{0.16em}{0ex}}^{94}\mathrm{Mo}({4}^{+})$ and $^{98}\mathrm{Tc}({6}^{+})\ensuremath{\rightarrow}\phantom{\rule{0.16em}{0ex}}^{98}\mathrm{Ru}({4}^{+})$ were found to depend strongly on ${g}_{\mathrm{A}}$, which makes them excellent candidates for the determination of the effective value of ${g}_{\mathrm{A}}$ with the spectrum-shape method (SSM). A strong ${g}_{\mathrm{A}}$ dependence is also seen in the spectrum of $^{96}\mathrm{Zr}({0}^{+})\ensuremath{\rightarrow}\phantom{\rule{0.16em}{0ex}}^{96}\mathrm{Nb}({6}^{+})$. This decay could be used for determining the quenching of ${g}_{\mathrm{A}}$ in sixth-forbidden decays in the future, when the measurement of the spectrum becomes experimentally feasible. The calculated shell-model electron spectra of the ground-state-to-ground-state decays of $^{87}\mathrm{Rb}$, $^{99}\mathrm{Tc}$, and $^{137}\mathrm{Cs}$ and the decay of $^{137}\mathrm{Cs}$ to the isomeric $11/{2}^{\ensuremath{-}}$ state in $^{137}\mathrm{Ba}$ were found to be in excellent agreement with the spectra previously calculated using the microscopic quasiparticle-phonon model. This is further evidence of the robust nature of the SSM observed in the previous studies.

Electron spectra in forbiddenβdecays and the quenching of the weak axial-vector coupling constantgA

Evolution of the electron spectra with the effective value of the weak axial-vector coupling constant ${g}_{\mathrm{A}}$ was followed for 26 first-, second-, third-, fourth- and fifth-forbidden ${\ensuremath{\beta}}^{\ensuremath{-}}$ decays of odd-$A$ nuclei by calculating the involved nuclear matrix elements (NMEs) in the framework of the microscopic quasiparticle-phonon model (MQPM). The next-to-leading-order terms were included in the $\ensuremath{\beta}$-decay shape factor of the electron spectra. The spectrum shapes of third- and fourth-forbidden nonunique decays were found to depend strongly on the value of ${g}_{\mathrm{A}}$, while first- and second-forbidden decays were mostly unaffected by the tuning of ${g}_{\mathrm{A}}$. The ${g}_{\mathrm{A}}$-driven evolution of the normalized $\ensuremath{\beta}$ spectra was found to be quite universal, largely insensitive to the small changes in the nuclear mean field and the adopted residual many-body Hamiltonian producing the excitation spectra of the MQPM. This makes the comparison of experimental and theoretical electron spectra, coined ``the spectrum-shape method'' (SSM), a robust tool for extracting information on the effective values of the weak coupling constants. In this exploratory work two new experimentally interesting decays for the SSM treatment were discovered: the ground-state-to-ground-state decays of $^{99}\mathrm{Tc}$ and $^{87}\mathrm{Rb}$. Comparing the experimental and theoretical spectra of these decays could shed light on the effective values of ${g}_{\mathrm{A}}$ and ${g}_{\mathrm{V}}$ for second- and third-forbidden nonunique decays. The measurable decay transitions of $^{135}\mathrm{Cs}$ and $^{137}\mathrm{Cs}$, in turn, can be used to test the SSM in different many-body formalisms. The present work can also be considered as a (modest) step towards solving the ${g}_{\mathrm{A}}$ problem of the neutrinoless double beta decay.

Spectrum-shape method and the next-to-leading-order terms of theβ-decay shape factor

Effective values of the axial-vector coupling constant ${g}_{\mathrm{A}}$ have lately attracted much attention due to the prominent role of ${g}_{\mathrm{A}}$ in determining the half-lives of double $\ensuremath{\beta}$ decays, in particular their neutrinoless mode. The half-life method, i.e., comparing the calculated half-lives to the corresponding experimental ones, is the most widely used method to access the effective values of ${g}_{\mathrm{A}}$. The present paper investigates the possibilities offered by a complementary method: the spectrum-shape method (SSM). In the SSM, comparison of the shapes of the calculated and measured $\ensuremath{\beta}$ electron spectra of forbidden nonunique $\ensuremath{\beta}$ decays yields information on the magnitude of ${g}_{\mathrm{A}}$. In parallel, we investigate the impact of the next-to-leading-order terms of the $\ensuremath{\beta}$-decay shape function and the radiative corrections on the half-life method and the SSM by analyzing the fourfold forbidden decays of $^{113}\mathrm{Cd}$ and $^{115}\mathrm{In}$ by using three nuclear-structure theory frameworks; namely, the nuclear shell model, the microscopic interacting boson-fermion model, and the microscopic quasiparticle-phonon model. The three models yield a consistent result, ${g}_{\mathrm{A}}\ensuremath{\approx}0.92$, when the SSM is applied to the decay of $^{113}\mathrm{Cd}$ for which $\ensuremath{\beta}$-spectrum data are available. At the same time the half-life method yields results which are in tension with each other and the SSM result.

$\beta $ Decay as a New Probe for the Low-energy E1 Strength

In this contribution, it is evaluated whether high Q-value β decays from mothers with low ground-state spin are suitable to probe the structure of 1− levels associated with the pygmy dipole response. A comparison of data from the exemplary 136I →136Xe β decay and the 136Xe(γ,γ′) reaction reveals that some 1− levels are populated in both reactions but with a different pattern. An investigation within the microscopic quasiparticle phonon model shows that the pattern is related to the population of different parts of the wave functions of these 1− levels establishing β decay as a novel probe.

Forbidden nonuniqueβdecays and effective values of weak coupling constants

Forbidden nonunique $\ensuremath{\beta}$ decays feature shape functions that are complicated combinations of different nuclear matrix elements and phase-space factors. Furthermore, they depend in a very nontrivial way on the values of the weak coupling constants, ${g}_{\mathrm{V}}$ for the vector part and ${g}_{\mathrm{A}}$ for the axial-vector part. In this work we include also the usually omitted second-order terms in the shape functions to see their effect on the computed decay half-lives and electron spectra ($\ensuremath{\beta}$ spectra). As examples we study the fourth-forbidden nonunique ground-state-to-ground-state ${\ensuremath{\beta}}^{\ensuremath{-}}$ decay branches of $^{113}\mathrm{Cd}$ and $^{115}\mathrm{In}$ using the microscopic quasiparticle-phonon model and the nuclear shell model. A striking new feature that is reported in this paper is that the calculated shape of the $\ensuremath{\beta}$ spectrum is quite sensitive to the values of ${g}_{\mathrm{V}}$ and ${g}_{\mathrm{A}}$ and hence comparison of the calculated with the measured spectrum shape opens a way to determine the values of these coupling constants. This article is designed to show the power of this comparison, coined spectrum-shape method (SSM), by studying the two exemplary $\ensuremath{\beta}$ transitions within two different nuclear-structure frameworks. While the SSM seems to confine the ${g}_{\mathrm{V}}$ values close to the canonical value ${g}_{\mathrm{V}}=1.0$, the values of ${g}_{\mathrm{A}}$ extracted from the half-life data and by the SSM emerge contradictory in the present calculations. This calls for improved nuclear-structure calculations and more measured data to systematically employ SSM for determination of the effective value of ${g}_{\mathrm{A}}$ in the future.

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

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.

Neutrino scattering off the stable cadmium isotopes: II. Charged-current processes

The present study is a continuation of our previous work (2015 J. Phys. G: Nucl. Part. Phys. 42 025106) on neutral-current supernova-neutrino processes in the stable cadmium isotopes. Here we concentrate on the charged-current scattering processes of neutrinos off the stable cadmium isotopes covering an energy range characteristic of supernova neutrinos. As a theory framework we adopt the quasiparticle random-phase approximation in its charge-changing mode (pnQRPA) and the microscopic quasiparticle-phonon model to construct the required nuclear wave functions of the odd–odd and odd–even isobars of the stable even–even reference cadmium isotopes, respectively. The cross sections of the charged-current neutrino and antineutrino scatterings off the stable cadmium isotopes are subsequently computed. The nuclear responses to supernova neutrinos are also estimated by folding the cross sections with neutrino-energy spectra including the effects of matter oscillations within an effective two-neutrino framework. The calculations indicate that the folded cross sections have mass-number dependencies that are different for neutrinos and antineutrinos, and that odd-mass nuclei have relatively large cross sections. The matter oscillations affect the cross sections strongly and it is found that the computed averaged cross sections for antineutrinos differ notably for the normal/inverted mass hierarchy. This could have interesting consequences for the experimental solution of the mass-hierarchy problem in future large-scale neutrino telescopes.

Neutrino scattering off the stable cadmium isotopes: neutral-current processes

In this work we present computed cross sections for the incoherent neutral-current neutrino scattering off the stable cadmium isotopes. The main focus is on supernova neutrinos. The nuclear states of the even-mass and odd-mass cadmium isotopes have been constructed using the quasiparticle random-phase approximation and the microscopic quasiparticle-phonon model, respectively. The computed cross sections are folded with suitably parametrized Fermi–Dirac distributions of the supernova (anti)neutrinos energies to obtain realistic estimates of the nuclear responses to these neutrinos.

Beta decay of 115Cd and its possible ultra-low Q-value branch

In this work we study the allowed and forbidden β −-decay transitions from 115Cd to 115In in the framework of the microscopic quasiparticle-phonon model (MQPM) using realistic single-particle model spaces and G-matrix-based effective interactions. Both the 1/2+ ground state and the 11/2− isomeric state in 115Cd decay to various final states in 115In. Results of the calculations are compared with experimental data on partial decay half-lives to probe the wave functions produced by the MQPM. Of special interest is the possible decay branch 1/2+ β 9/2+ that is fourth-forbidden non-unique with a possible ultra-low Q-value associated with it. Accurate measurement of the ground-state-to-ground-state Q-value by, e.g., the Penning trap techniques, is urged to verify the existence of this decay transition. Such ultra-low Q-value transitions could be valuable in measurements of the electron-neutrino mass and studies of the interference of atomic effects.

Charged-current neutrino-nucleus scattering off95,97Mo

Background: Reliable cross sections for the neutrino-nucleus scattering off relevant nuclei for supernova neutrinos are essential for various applications in neutrino physics and astrophysics (e.g., supernova mechanisms). Studies of the nuclear responses for the stable molybdenum isotopes are of great interest for the planned MOON (Mo Observatory of Neutrinos) experiment.Purpose: The purpose of the present work is, thus, to perform a detailed study of the charged-current nuclear responses to supernova neutrinos for the stable odd molybdenum isotopes. A special effort will be devoted to discuss in detail the structures of the most relevant final states in the corresponding proton-odd nucleus.Method: The cross sections are computed by using the well-established framework for studies of semileptonic processes in nuclei developed by Donnelly and Walecka. The nuclear wave functions of the initial and the final nuclear states are computed by using the microscopic quasiparticle-phonon model. The nuclear responses to supernova neutrinos are subsequently estimated by folding the cross sections with realistic energy profiles for the incoming neutrinos.Results: We present results for the cross sections of the charged-current neutrino and antineutrino scatterings off ${}^{95}\text{Mo}$ and ${}^{97}\text{Mo}$. Nuclear responses to supernova neutrinos (both nonoscillating and oscillating ones) are also given. The inclusion of neutrino oscillations enhances significantly the neutrino and antineutrino cross sections.Conclusions: We have found that the most important transitions are the Gamow-Teller--like ones which are mediated by the ${1}^{+}$ multipole. Furthermore, the three-quasiparticle degrees of freedom are essential in order to describe quantitatively the neutrino-nucleus scattering off odd open-shell nuclei.

Theoretical analysis of the possible ultra-low-Q-value decay branch of 135Cs

We have investigated the feasibility of observing an ultra-low-Q-value beta-decay branch of 135Cs by applying the microscopic quasiparticle–phonon model with a realistic two-body nuclear interaction. This work was motivated by an earlier combined experimental and theoretical work on decays of 115In. The inaccuracy of the ground-state-to-ground-state Q value limits our ability to draw definite conclusions, and therefore modern precision measurements for it are called for. We present the computed partial half-lives of each channel for the most likely ranges of Q values.

The response of 95,97Mo to supernova neutrinos

Abstract Knowledge about nuclear responses to neutrinos is essential for both astrophysical applications and studies of neutrino properties. We perform in this paper calculations of the cross sections for neutral-current neutrino scattering off the odd A = 95 , 97 Mo isotopes for energies appropriate for the detection of supernova neutrinos. Both the incoherent and coherent contributions to the cross sections are evaluated. The prominently contributing nuclear final states are identified and analysed. We employ the microscopic quasiparticle-phonon model (MQPM) to construct the wave functions of the initial and final nuclear states. The response of the aforementioned nuclei to supernova neutrinos are computed by folding the obtained cross sections with a two-parameter Fermi–Dirac distribution. The sensitivity of the calculated nuclear responses to the adopted supernova model is also discussed.

On the decay of the Jπ = 11/2−, T1/2 = 38.9 h isomer in 133Ba: search for the E5 transition and verification of the EC branch

This paper presents a search for the competing 11/2− → 1/2+ E5 branch to the main 11/2− → 3/2+ M4 transition from the T1/2 = 39 h, Jπ = 11/2− isomeric state in 133Ba. An upper limit of 1.8 × 10−5 could be established for the E5/M4 intensity ratio. In addition, a longstanding controversy in the EC decay of the same isomer was resolved: only one EC branch to the 11/2+ state in 133Cs was observed. The shell-model structures of the involved states in 133Ba and 133Cs were studied with the microscopic quasiparticle-phonon model. Good agreement with the decay rates B(λ) was obtained. In particular, the B(M4) value is well reproduced and further only one low-lying 11/2 state could be identified in the latter nuclide, supporting the experimental results.

MQPM description of the structure and beta decays of the odd [formula omitted] Mo and Tc isotopes

The odd-mass isotopes A = 95 , 97 of molybdenum are of interest for neutrino-physics applications. The microscopic quasiparticle-phonon model (MQPM) is used to calculate energy and decay characteristics of these nuclei and their beta-decay partners ( Tc 95 and Tc 97 ). A realistic single-particle valence space and two-body interaction are used in the calculations. The computed results are compared with available data. The obtained energy spectra are also compared with earlier calculations. We present the first ever calculations for the rates of allowed and forbidden β + / EC decay transitions in these nuclei. In general our computed numbers agree rather well with the available data.

Microscopic structure of low-lying states inOs188,190,192

The phonon and quasiparticle structure of the low-lying states in $^{188,190,192}\mathrm{Os}$ is investigated within the microscopic quasiparticle-phonon model. An overall agreement with the data is obtained for energies and transitions. The properties of the ${0}^{+}$ states are found to be correlated with the evolution of the nuclear shape toward the $\ensuremath{\gamma}$-soft region. Special attention is devoted at the ${4}_{3}^{+}$ state. This state is found to be composed of a large double-$\ensuremath{\gamma}$ phonon component coexisting with an even larger one-phonon hexadecapole piece. Such a mixed phonon structure explains the observed, apparently contradictory, properties of the ${4}_{3}^{+}$ states in Os isotopes.

Microscopic quasiparticle–phonon description of beta decays of 113Cd and 115In using proton–neutron phonons

The fourth-forbidden non-unique ground-state-to-ground-state beta decays of 113Cd and 115In are calculated using a realistic microscopic two-body interaction and a realistic single-particle model space. To describe the involved initial and final nuclear states we introduce a proton–neutron variant of the microscopic quasiparticle–phonon model (MQPM), the proton–neutron MQPM (pnMQPM). The states of the pnMQPM are created by coupling quasiparticles with phonons of the proton–neutron quasiparticle random-phase approximation (pnQRPA). The computed half-lives and logft values are found to be in excellent agreement with experimental data. Computed beta spectra of the decays are also given.