Two-neutrino ββ\beta\beta decay of 136^{136}Xe to the first excited 0+0^+ state in 136^{136}Ba

We calculate the nuclear matrix element for the two-neutrino $\beta\beta$ decay of $^{136}$Xe into the first excited $0^+$ state of $^{136}$Ba. We use different many-body methods: the quasiparticle random-phase approximation (QRPA) framework, the nuclear shell model, the interacting boson model (IBM-2), and an effective field theory (EFT) for $\beta$ and $\beta\beta$ decays. While the QRPA suggests a decay rate at the edge of current experimental limits, the shell model points to a half-life about two orders of magnitude longer. The predictions of the IBM-2 and the EFT lie in between, and the latter provides systematic uncertainties at leading order. An analysis of the running sum of the nuclear matrix element indicates that subtle cancellations between the contributions of intermediate states can explain the different theoretical predictions. For the EFT, we also present results for two-neutrino $\beta\beta$ decays to the first excited $0^+$ state in other nuclei.Comment: 9 pages, 4 figures, 1 tabl

Arviointiuudistuksen alkutaipaleella : Perusopetuksen päättöarviointitutkimuksen loppuraportti

Opetus- ja kulttuuriministeriön rahoittamassa tutkimushankkeessa on tutkittu perusopetuksen päättöarviointiuudistuksen käyttöönottoa. Tutkimus oli osa opetus- ja kulttuuriministeriön vuosina 2020–2022 toteuttamaa varhaiskasvatuksen ja perusopetuksen laatua ja tasa-arvoa parantavaa Oikeus Oppia -kehittämisohjelmaa. Tutkimuksen toteutti Jyväskylän yliopiston Koulutuksen tutkimuslaitoksen ja Helsingin yliopiston Kasvatustieteellisen tiedekunnan muodostama tutkimusryhmä. Tutkimushankkeeseen sisältyi kolme osa-aluetta: 1) opetustoimen johdon ja rehtoreiden näkökulma uudistukseen, 2) opettajien näkökulma uudistukseen sekä 3) perusopetuksen päättöarvosanojen muutokset. Tutkimus rajattiin viiteen oppiaineeseen: äidinkieli ja kirjallisuus, matematiikka, fysiikka, englanti ja historia. Tutkimushankkeen tulokset perustuvat opetustoimen johdolle, rehtoreille ja opettajille tehtyihin kyselyihin ja haastatteluihin sekä rekisteriaineistoon perusopetuksen päättöarvosanoista. Loppuraportissa on kuvattu, miten uudistusprosessi on kunnissa ja kouluissa edennyt, miten opetustoimen henkilöstö kokee uudistuksen, miten he tulkitsevat uusia arviointilinjauksia ja päättöarvioinnin kriteereitä sekä miten päättöarvosanat ovat muuttuneet uudistuksen jälkeen. Raportissa esitetään myös suosituksia siitä, miten arviointilinjauksia ja päättöarvioinnin kriteereitä tulisi kehittää jatkossa

Recent results on heavy-ion induced reactions of interest for neutrinoless double beta decay at INFN-LNS

Abstract. The possibility to use a special class of heavy-ion induced direct reactions, such as double charge exchange reactions, is discussed in view of their application to extract information that may be helpful to determinate the nuclear matrix elements entering in the expression of neutrinoless double beta decay halflife. The methodology of the experimental campaign presently running at INFN - Laboratori Nazionali del Sud is reported and the experimental challenges characterizing such activity are describe

NURE: An ERC project to study nuclear reactions for neutrinoless double beta decay

Neutrinoless double beta decay (0νββ) is considered the best potential resource to access the absolute neutrino mass scale. Moreover, if observed, it will signal that neutrinos are their own anti-particles (Majorana particles). Presently, this physics case is one of the most important research “beyond Standard Model” and might guide the way towards a Grand Unified Theory of fundamental interactions. Since the 0νββ decay process involves nuclei, its analysis necessarily implies nuclear structure issues. In the NURE project, supported by a Starting Grant of the European Research Council (ERC), nuclear reactions of double charge-exchange (DCE) are used as a tool to extract information on the 0νββ Nuclear Matrix Elements. In DCE reactions and ββ decay indeed the initial and final nuclear states are the same and the transition operators have similar structure. Thus the measurement of the DCE absolute cross-sections can give crucial information on ββ matrix elements. In a wider view, the NUMEN international collaboration plans a major upgrade of the INFN-LNS facilities in the next years in order to increase the experimental production of nuclei of at least two orders of magnitude, thus making feasible a systematic study of all the cases of interest as candidates for 0νββ

New results from the NUMEN project

NUMEN aims at accessing experimentally driven information on Nuclear Matrix Elements (NME) involved in the half-life of the neutrinoless double beta decay (0νββ), by high-accuracy measurements of the cross sections of Heavy Ion (HI) induced Double Charge Exchange (DCE) reactions. First evidence about the possibility to get quantitative information about NME from experiments is found for the (18O,18Ne) and (20Ne,20O) reactions. Moreover, to infer the neutrino average masses from the possible measurement of the half-life of 0νββ decay, the knowledge of the NME is a crucial aspect. The key tools for this project are the high resolution Superconducting Cyclotron beams and the MAGNEX magnetic spectrometer at INFN Laboratori Nazionali del Sud in Catania (Italy). The measured cross sections are extremely low, limiting the present exploration to few selected isotopes of interest in the context of typically low-yield experimental runs. A major upgrade of the LNS facility is foreseen in order to increase the experimental yield of at least two orders of magnitude, thus making feasible a systematic study of all the cases of interest. peerReviewe

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.peerReviewe

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.peerReviewe

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.peerReviewe

Rare weak decays and neutrino mass

The question whether neutrinos are Majorana fermions (i.e., their own anti-particles) remains among the most fundamental open questions of subatomic physics. If neutrinos are Majorana particles it would revolutionize our understanding of physics. Although neutrinoless double beta decay, 0νββ, was proposed more than 80 years ago to establish the nature of neutrinos, it remains the most sensitive probe into the non-conservation of lepton number. 0νββ-decay is a postulated extremely slow and yet unobserved radioactive process in which two neutrons (or protons) inside a nucleus transform into two protons (or neutrons) emitting two electrons (or positrons), respectively, but no neutrinos. Its observation would be a breakthrough in the description of elementary particles and would provide fundamental information on the neutrino masses, their nature, and origin. In this paper double beta decay, its connection to neutrino mass, and mechanisms beyond the standard mass mechanism are discussed from a theoretical point of view. The current situation is then addressed by combining theoretical results with recent experimental limits.peerReviewe