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

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-β decay using these sets. Our results are compared with other theoretical calculations and experimental occupancies, when available.peerReviewe

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.peerReviewe

Collective features of Cr and Fe isotopes

The question of the sudden increase of collectivity in neutron-rich nuclei when approaching N = 40 has recently interested both experimentalists and theorists. In this paper we study the development of collectivity along the chromium and iron isotopic chains. The calculations are performed within two different perspectives, namely, the proton-neutron interacting boson model (IBM-2) and interacting shell model (ISM) and compared with the available experimental data. The onset of collectivity is studied through nuclear quantities and observables that suggest differences in the nuclear structure of Cr and Fe isotopical chains. Furthermore, a prediction for the shape transition from a spherical vibrator to γ -soft rotor with nucleus 58Cr standing at the critical point is discussed.peerReviewe

0νββ and 2νββ nuclear matrix elements in the interacting boson model with isospin restoration

We introduce a method for isospin restoration in the calculation of nuclear matrix elements (NMEs) for 0νββ and 2νββ decay within the framework of the microscopic interacting boson model (IBM-2). With this method, we calculate the NMEs for all processes of interest in 0νβ−β− and 2νβ−β− and in 0νβ+β+, 0νECβ+, R0νECEC, 2νβ+β+, 2νECβ+, and 2νECEC. With this method, the Fermi matrix elements for 2νββ vanish, and those for 0νββ are considerably reduced.peerReviewe

Quenching of gA and its impact in double beta decay

The theory of double beta decay is briefly reviewed. The most recent (2015) results for 0νβ −β − nuclear matrix elements in the interacting boson model (IBM-2) with light and heavy neutrino exchange are given for all nuclei of interest from 48Ca to 238U. The question of quenching of the axial vector coupling constant gA in nuclei is discussed. Possible additional scenarios, such as Majoron emission, and mechanisms, such as sterile neutrino exchanges, are also discussed.nonPeerReviewe

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

Effective values of the axial-vector coupling constant gA have lately attracted much attention due to the prominent role of gA in determining the half-lives of double β 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 gA. 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 β electron spectra of forbidden nonunique β decays yields information on the magnitude of gA. In parallel, we investigate the impact of the next-to-leading-order terms of the β-decay shape function and the radiative corrections on the half-life method and the SSM by analyzing the fourfold forbidden decays of 113Cd and 115In 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, gA≈0.92, when the SSM is applied to the decay of 113Cd for which β-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.peerReviewe

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, 0νECEC. 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 124Xe, 152Gd, 156Dy, 164Er, and 180W. From the PF and NME we calculate the expected half-lives and obtain results that are of the same order as those of 0νβ+β+ decay, but considerably longer than those of 0νβ−β− decay.peerReviewe

Short-range neutrinoless double beta decay mechanisms

Neutrinoless double beta decay can significantly help to shed light on the issue of nonzero neutrino mass, as the observation of this lepton-number-violating process would imply that neutrinos are Majorana particles. However, the underlying interaction does not have to be as simple as the standard neutrino mass mechanism. The entire variety of neutrinoless double beta decay mechanisms can be approached effectively. In this work, we focus on a theoretical description of short-range effective contributions to neutrinoless double beta decay, which are equivalent to nine-dimensional effective operators incorporating the appropriate field content. We give a detailed derivation of the nuclear matrix elements and phase-space factors corresponding to individual terms of the effective Lagrangian. Using these, we provide general formulas for the neutrinoless double beta decay half-life and angular correlation of the outgoing electrons.peerReviewe

PISA 2022 ensituloksia

Kolmen vuoden välein toteutettava PISA-tutkimusohjelma, jota koronapandemian vuoksi jouduttiin siirtämään vuodella alkuperäisestä aikataulusta, toteutettiin vuonna 2022 kahdeksannen kerran. Tutkimuksessa selvitetään, miten 15-vuotiaat nuoret hallitsevat tulevaisuuden kannalta keskeisiä avaintaitoja, millaiset tekijät ovat yhteydessä näihin taitoihin ja millaisia muutoksia osaamisessa on havaittavissa verraten aiempiin tutkimuskierroksiin. Ensitulokset-raportin tulokset painottuvat erityisesti kolmatta kertaa pääarviointialueena olevaan matematiikan osaamiseen sekä siihen yhteydessä oleviin oppimisen kannalta keskeisiin taustatekijöihin. Siten voidaan luotettavasti tutkia lähes 20 vuoden aikana tapahtuneita muutoksia matematiikan osaamisessa. Lukutaitoa sekä luonnontieteiden osaamista tarkastellaan matematiikan osaamisen ohella sivuarviointialueina. Tällä kierroksella tarkastellaan osaamisen lisäksi aiempien tutkimuskierrosten tapaan muun muassa oppilaiden suhtautumista opiskelua kohtaan, oppimisympäristöä, oppilaiden hyvinvointia, mutta myös koronapandemian yhteyttä oppimistuloksiin. PISA 2022 -tutkimukseen osallistui 10 239 oppilasta 241 koulusta. Aiheesta on tehty myös esite: PISA 2022 ensituloksia lyhyestiJulkaisu on päivitetty 20.12.2023, sivut 61, 64–70 ja 132

The NUMEN project @ LNS : Status and perspectives

The aim of the NUMEN project is to access the Nuclear Matrix Elements (NME), involved in the half life of the neutrinoless double beta decay (0νββ), by measuring the cross sections of Heavy Ions (HI) induced Double Charge Exchange (DCE) reactions with high accuracy. First evidence of the possibility to get quantitative information about NME from experiments is shown in the reaction 40Ca(18O,18Ne)40Ar at 270 MeV, performed with MAGNEX spectrometer using Superconducting Cyclotron (CS) beams at INFN - Laboratory Nazionali del Sud (LNS) in Catania. Preliminary tests on 116Sn and 116Cd target are already performed. High beam intensity is the new frontiers for these studies.peerReviewe