Comparative Analysis of Nuclear Matrix Elements of 0νβ+β+ Decay and Muon Capture in 106Cd

Comparative analyses of the nuclear matrix elements (NMEs) related to the 0νβ+β+ decay of 106Cd to the ground state of 106Pd and the ordinary muon capture (OMC) in 106Cd are performed. This is the first time the OMC NMEs are studied for a nucleus decaying via positron-emitting/electron-capture modes of double beta decay. All the present calculations are based on the proton-neutron quasiparticle random-phase approximation with large no-core single-particle bases and realistic two-nucleon interactions. The effect of the particle-particle interaction parameter gpp of pnQRPA on the NMEs is discussed. In the case of the OMC, the effect of different bound-muon wave functions is studied. peerRevie…

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

Abstract The NUMEN project aims at accessing experimentally driven information on Nuclear Matrix Elements (NME) involved in the half-life of the neutrinoless double beta decay (0νββ). In this view measurements of Heavy Ion (HI) induced Double Charge Exchange (DCE) reaction cross sections are performed with high-accuracy. In particular, the (18O,18Ne) and (20Ne,20O) reactions are used as tools for β+β+ and β-β- decays, respectively. In the experiments, performed at INFN - Laboratory Nazionali del Sud (LNS) in Catania, the beams are accelerated by the Superconducting Cyclotron (CS) and the reaction ejectiles are detected the MAGNEX magnetic spectrometer. The measured cross sections are challe…

β -decay rates of Rh115,117 into Pd115,117 isotopes in the microscopic interacting boson-fermion model

The structure of odd-$A ^{115,117}\mathrm{Rh}$ and $^{115,117}\mathrm{Pd}$ isotopes is studied by means of the neutron-proton interacting boson-fermion model (IBFM-2). ${J}^{P}={\frac{1}{2}}^{+}$ quantum number assignment for the $^{115,117}\mathrm{Pd}$ ground states is critically discussed and the predicted energy levels are compared to the existing experimental data. The resulting nuclear wave functions are used to compute the $\ensuremath{\beta}$-decay $ft$ values of the transitions from $^{115,117}\mathrm{Rh}$ to $^{115,117}\mathrm{Pd}$ in the microscopic IBFM-2 and the results compared with the data.

Majorana parameters of the interacting boson model of nuclear structure and their implication for 0νββ decay

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.

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 m…

Nuorten voimavarat, oppimista vaikeuttavat tekijät ja kilpailullisuus oppimista määrittävinä tekijöinä PISA 2018 -tutkimuksessa

Tulevaisuuden avaintaidot puntarissa: Kahdeksannen luokan oppilaiden matematiikan ja luonnontieteiden osaaminen: kansainvälinen TIMSS 2019 -tutkimus Suomessa

TIMSS (Trends in International Mathematics and Science Study) on kansainvälinen koulutuksen arvioinnin tutkimusohjelma, jossa joka neljäs vuosi arvioidaan neljäsja kahdeksasluokkalaisten oppilaiden matematiikan ja luonnontieteiden osaamista. Kansainvälinen arviointijärjestö IEA (International Association for the Evaluation of Educational Achievement) on johtanut vertailevan arvioinnin tutkimuksia jo 1960-luvulta lähtien. TIMSStutkimusohjelma alkoi vuonna 1995, ja Suomi osallistui tähän tutkimukseen ensimmäisen kerran vuonna 1999. Vuoden 2011 tutkimuskerralla Suomesta arviointiin osallistuivat sekä neljäs- että kahdeksasluokkalaiset oppilaat, mutta viimekertaisessa TIMSS 2015 -arvioinnissa m…

Perustaidoista vauhtia koulutielle: Neljännen luokan oppilaiden matematiikan ja luonnontieteiden osaaminen: kansainvälinen TIMSS 2019 -tutkimus Suomessa

TIMSS (Trends in International Mathematics and Science Study) on kansainvälinen koulutuksen arvioinnin tutkimusohjelma, jossa joka neljäs vuosi arvioidaan neljäs- ja kahdeksasluokkalaisten oppilaiden matematiikan ja luonnontieteiden osaamista. Kansainvälinen arviointijärjestö IEA (International Association for the Evaluation of Educational Achievement) on johtanut vertailevan arvioinnin tutkimuksia jo 1960-luvulta lähtien. TIMSS-tutkimusohjelma alkoi vuonna 1995, ja Suomi osallistui tähän tutkimukseen ensimmäisen kerran vuonna 1999. Vuoden 2011 tutkimuskerralla Suomesta arviointiin osallistuivat sekä neljäs- että kahdeksasluokkalaiset oppilaat, mutta edellisen kierroksen TIMSS 2015 -arvioin…

Analysis of light neutrino exchange and short-range mechanisms in 0νββ decay

Neutrinoless double beta decay (0νββ) is a crucial test for lepton number violation. Observation of this process would have fundamental implications for neutrino physics, theories beyond the Standard Model and cosmology. Focusing on so-called short-range operators of 0νββ and their potential interplay with the standard light Majorana neutrino exchange, we present the first complete calculation of the relevant nuclear matrix elements, performed within the interacting boson model (IBM-2). Furthermore, we calculate the relevant phase space factors using exact Dirac electron wave functions, taking into account the finite nuclear size and screening by the electron cloud. The obtained numerical r…

β-decay rates of 115,117Rh into 115,117Pd isotopes in the microscopic interacting boson-fermion model

The structure of odd-A 115,117Rh and 115,117Pd isotopes is studied by means of the neutron-proton interacting boson-fermion model (IBFM-2). JP=12+ quantum number assignment for the 115,117Pd ground states is critically discussed and the predicted energy levels are compared to the existing experimental data. The resulting nuclear wave functions are used to compute the β-decay ft values of the transitions from 115,117Rh to 115,117Pd in the microscopic IBFM-2 and the results compared with the data. peerReviewed

First microscopic evaluation of spin-dependent WIMP-nucleus scattering off 183W

We perform the first consistent calculation of elastic-scattering and inelastic-scattering structure functions for spin-dependent WIMP-nucleus scattering for 183W in a microscopic nuclear-theory framework. The nuclear structure calculations are performed in the microscopic interacting boson-fermion model (IBFM-2). Our results show that while 183W is very insensitive to spin-dependent elastic scattering, the structure function for inelastic scattering is quite sizable at small momentum transfers. Moreover, to our knowledge 183W provides the first studied case where inelastic scattering can compete with elastic scattering as the primary detection signal. peerReviewed

Measuring nuclear reaction cross sections to extract information on neutrinoless double beta decay

Neutrinoless double beta decay (0v\b{eta}\b{eta}) 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 0v\b{eta}\b{eta} 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 extr…

Rare weak decays and neutrino mass

Abstract 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 neutrino…

Microscopic nuclear-structure calculations for the low-lying collective states in even-even nuclei

Fascinating puzzle called double beta decay

The question of whether neutrinos are Majorana or Dirac particles and what are their average masses remains one of the most fundamental problems in physics today. Observation of neutrinoless double beta decay (0νββ) would verify the Majorana nature of the neutrino and constrain the absolute scale of the neutrino mass spectrum. 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. Recent calculations of PSF and NME will be reviewed together with comparison to other available results. These calculations serve the p…

Analysis of light neutrino exchange and short-range mechanisms in 0νββ decay

Neutrinoless double beta decay (0νββ) is a crucial test for lepton number violation. Observation of this process would have fundamental implications for neutrino physics, theories beyond the Standard Model and cosmology. Focusing on so-called short-range operators of 0νββ and their potential interplay with the standard light Majorana neutrino exchange, we present the first complete calculation of the relevant nuclear matrix elements, performed within the interacting boson model (IBM-2). Furthermore, we calculate the relevant phase space factors using exact Dirac electron wave functions, taking into account the finite nuclear size and screening by the electron cloud. The obtained numerical r…

Double beta decay and the quest for Majorana neutrinos

Abstract 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 f…

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

Neutrinoless double beta decay (0{\nu}\b{eta}\b{eta}) is considered the best potential resource to determine the absolute neutrino mass scale. Moreover, if observed, it will signal that the total lepton number is not conserved and neutrinos are their own anti-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 \b{eta}\b{eta} decay process involves nuclei, its analysis necessarily implies nuclear structure issues. The 0{\nu}\b{eta}\b{eta} decay rate can be expressed as a product of independent factors: the phase-space factors, the nuclear matrix elemen…

Ordinary Muon Capture on 136Ba : Comparative Study Using the Shell Model and pnQRPA

In this work, we present a study of ordinary muon capture (OMC) on 136136Ba, the daughter nucleus of 136136Xe double beta decay (DBD). The OMC rates at low-lying nuclear states (below 1 MeV of excitation energy) in 136136Cs are assessed by using both the interacting shell model (ISM) and proton–neutron quasiparticle random-phase approximation (pnQRPA). We also add chiral two-body (2BC) meson-exchange currents and use an exact Dirac wave function for the captured s-orbital muon. OMC can be viewed as a complementary probe of the wave functions in 136136Cs, the intermediate nucleus of the 136136Xe DBD. At the same time, OMC can be considered a powerful probe of the effective values of weak axi…

Spin-dependent WIMP-nucleus scattering off 125Te, 129Xe, and 131Xe in the microscopic interacting boson-fermion model

We perform calculations of structure functions for elastic and inelastic spin-dependent scattering of weakly interacting massive particles (WIMPs) off 125Te, 129Xe, and 131Xe. The nuclear structure calculations are performed in the microscopic interacting boson-fermion model (IBFM-2). In our calculations we employ one-body and leading long-range two-body WIMP-nucleus currents derived from chiral effective field theory. We demonstrate that the relevant matrix elements can be reliably computed in the IBFM-2, which will allow investigation of heavy deformed nuclei previously inaccessible to theoretical calculations. peerReviewed