Beta Decay Data Research Articles

Impact of nuclear matrix element calculations for current and future neutrinoless double beta decay searches

Nuclear matrix elements (NME) are a crucial input for the interpretation of neutrinoless double beta decay data. We consider a representative set of recent NME calculations from different methods and investigate the impact on the present bound on the effective Majorana mass mββ by performing a combined analysis of the available data as well as on the sensitivity reach of future projects. A crucial role is played by the recently discovered short-range contribution to the NME, induced by light Majorana neutrino masses. Depending on the NME model and the relative sign of the long- and short-range contributions, the current 3σ bound can change between mββ< 40 meV and 600 meV. The sign-uncertainty may either boost the sensitivity of next-generation experiments beyond the region for mββ predicted for inverted mass ordering or prevent even advanced setups to reach this region. Furthermore, we study the possibility to distinguish between different NME calculations by assuming a positive signal and by combining measurements from different isotopes. Such a discrimination will be impossible if the relative sign of the long- and short-range contribution remains unknown, but can become feasible if mββ ≳ 40 meV and if the relative sign is known to be positive. Sensitivities will be dominated by the advanced 76Ge and 136Xe setups assumed here, but NME model-discrimination improves if data from a third isotope is added, e.g., from 130Te or 100Mo.

Semileptonic tau decays beyond the Standard Model

Hadronic τ decays are studied as probe of new physics. We determine the dependence of several inclusive and exclusive τ observables on the Wilson coefficients of the low-energy effective theory describing charged-current interactions between light quarks and leptons. The analysis includes both strange and non-strange decay channels. The main result is the likelihood function for the Wilson coefficients in the tau sector, based on the up-to-date experimental measurements and state-of-the-art theoretical techniques. The likelihood can be readily combined with inputs from other low-energy precision observables. We discuss a combination with nuclear beta, baryon, pion, and kaon decay data. In particular, we provide a comprehensive and model-independent description of the new physics hints in the combined dataset, which are known under the name of the Cabibbo anomaly.

Extensive Study of the Quality of Fission Yields from Experiment, Evaluation and GEF for Antineutrino Studies and Applications

The understanding of the antineutrino production in fission and the theoretical calculation of the antineutrino energy spectra in different, also future, types of fission reactors rely on the application of the summation method, where the individual contributions from the different radioactive nuclides that undergo a beta decay are estimated and summed up. The most accurate estimation of the independent fission-product yields is essential to this calculation. This is a complex task because the yields depend on the fissioning nucleus and on the energy spectrum of the incident neutrons.In the present contribution, the quality of different sources of information on the fission yields is investigated, and the benefit of a combined analysis is demonstrated. The influence on antineutrino predictions is discussed.In a systematic comparison, the quality of fission-product yields emerging from different experimental techniques is analyzed. The traditional radiochemical method, which is almost exclusively used for evaluations, provides an unambiguous identification in Z and A, but it is restricted to a limited number of suitable targets, is slow, and the accuracy suffers from uncertainties in the spectroscopic nuclear properties. Experiments with powerful spectrometers, for example at LOHENGRIN, provide very accurate mass yields and a Z resolution for light fission products from thermal-neutron-induced fission of a few suitable target nuclei.On the theoretical side, the general fission model GEF has been developed. It combines a few general theorems, rules and ideas with empirical knowledge. GEF covers almost all fission observables and is able to reproduce measured data with high accuracy while having remarkable predictive power by establishing and exploiting unexpected systematics and hidden regularities in the fission observables. In this article, we have coupled for the first time the GEF predictions for the fission yields to fission-product beta-decay data in a summation calculation of reactor antineutrino energy spectra. The first comparisons performed between the spectra from GEF and those obtained with the evaluated nuclear databases exhibited large discrepancies that highlighted the exigency of the modelisation of the antineutrino spectra and showing their usefulness in the evaluation of nuclear data. Additional constraints for the GEF model were thus needed in order to reach the level of accuracy required by the antineutrino energy spectra. The combination of a careful study of the independent isotopic yields and the adjunction of the LOHENGRIN fission-yield data as additional constraints led to a substantially improved agreement between the antineutrino spectra computed with GEF and with the evaluated data. The comparison of inverse beta-decay yields computed with GEF with those measured by the Daya Bay experiment shows the excellent level of predictiveness of the GEF model for the fundamental or applied antineutrino physics.The main results of this study are:–an improved agreement between the antineutrino energy spectra obtained with the newly tuned GEF model and the JEFF-3.1.1 and JEFF-3.3 fission yields for the four main contributors to fission in standard power reactors;–indications for shortcomings of mass yields for 241Pu(nth, f) and other systems in current evaluations;–a demonstration of the benefit from cross-checking the results of different experimental approaches and GEF for improving the quality of nuclear data;–an analysis of the sources of uncertainties and erroneous results from different experimental approaches;–the capacity of GEF for predicting the fission yields (and other observables) in cases (in terms of fissioning systems and excitation energies) which are presently not accessible to experiment;–predictions of antineutrino energy spectra that aim to assess the prospects for reactor monitoring, and based on the GEF fission yields associated with the beta-decay data of the most recent summation model.

A High-Resolution Study of the 110Tc → 110Ru → 110Rh → 110Pd Decay Chain with the GRETINA Array

Spectroscopic data, such as precise γ-ray branching and E2/M1 multipole-mixing ratios, provide vital constraints when performing multi-dimensional Coulomb-excitation analyses. Consequently, as part of our new Coulomb-excitation campaign aimed at investigating the role of exotic non-axial (triaxial) deformations in the unstable refractory Ru-Mo isotopes, additional beta-decay data was obtained. These measurements make use of ANL’s CARIBU facility, which provides intense beams of radioactive refractory isotopes along with the excellent efficiency and angular resolution of the GRETINA γ-ray tracking array. In this article, we report on the analysis of the A = 110 decay chain, focussing on the identification of previously unreported states in 110Ru following the decay of 110Tc.

Searching for New Physics in Two-Neutrino Double Beta Decay.

Motivated by nonzero neutrino masses and the possibility of new physics discovery, a number of experiments search for neutrinoless double beta decay. While hunting for this hypothetical nuclear process, a significant amount of two-neutrino double beta decay data have become available. Although these events are regarded and studied mostly as the background of neutrinoless double beta decay, they can also be used to probe physics beyond the standard model. In this Letter, we show how the presence of right-handed leptonic currents would affect the energy distribution and angular correlation of the outgoing electrons in two-neutrino double beta decay. Consequently, we estimate constraints imposed by currently available data on the existence of right-handed neutrino interactions without having to assume their nature. In this way, our results complement the bounds coming from the nonobservation of neutrinoless double beta decay as they limit also the exotic interactions of Dirac neutrinos. We perform a detailed calculation of two-neutrino double beta decay under the presence of exotic (axial-) vector currents, and we demonstrate that current experimental searches can be competitive to existing limits.

Analysis of beta-decay data acquired at the Physikalisch-Technische Bundesanstalt: Evidence of a solar influence

According to an article entitled Disproof of solar influence on the decay rates of 90Sr/90Y by Kossert and Nähle of the Physikalisch-Technische Bundesanstalt (PTB) [1], the PTB measurements show no evidence of variability. We show that, on the contrary, those measurements reveal strong evidence of variability, including an oscillation at 11 year−1 that is suggestive of an influence of internal solar rotation. An analysis of radon beta-decay data acquired at the Geological Survey of Israel (GSI) Laboratory for the same time interval yields strong confirmation of this oscillation.

Precision Mass Measurements of ^{129-131}Cd and Their Impact on Stellar Nucleosynthesis via the Rapid Neutron Capture Process.

Masses adjacent to the classical waiting-point nuclide ^{130}Cd have been measured by using the Penning-trap spectrometer ISOLTRAP at ISOLDE/CERN. We find a significant deviation of over 400keV from earlier values evaluated by using nuclear beta-decay data. The new measurements show the reduction of the N=82 shell gap below the doubly magic ^{132}Sn. The nucleosynthesis associated with the ejected wind from type-II supernovae as well as from compact object binary mergers is studied, by using state-of-the-art hydrodynamic simulations. We find a consistent and direct impact of the newly measured masses on the calculated abundances in the A=128-132 region and a reduction of the uncertainties from the precision mass input data.

Comparative study of beta-decay data for eight nuclides measured at the Physikalisch-Technische Bundesanstalt

We present the results of time-series analyses of data, kindly provided by the Physikalisch-Technische Bundesanstalt, concerning the beta-decays of Ag108, Ba133, Cs137, Eu152, Eu154, Kr85, Ra226, and Sr90. From measurements of the detector currents, we find evidence of annual oscillations (especially for Ra226), and for several solar r-mode oscillations. It is notable that the frequencies of these r-mode oscillations correspond to exactly the same sidereal rotation rate (12.08year−1) that we have previously identified in r-mode oscillations detected in both Mt Wilson solar diameter data and Lomonosov Moscow State University Sr90 beta-decay data. Ba133 is found to be anomalous in that current measurements for this nuclide have a much larger variation (by 4σ) than those of the other nuclides. It is interesting that analysis of variability measurements in the PTB files yields strong evidence for an oscillation for Ba133 but only weak evidence for Ra226.

A new cluster model interpretation of the anomalous lifetime of 14C

A new cluster model solution to the long-standing nuclear structure problem of describing the anomalously long lifetime of 14C is presented. Related beta-decay data for 14O to states in 14N, gamma-decay data between low-lying positive parity states in 14N and the elastic and inelastic magnetic dipole electron scattering from 14N data are all shown to be very accurately described by the model. The shapes of the beta spectra for the A = 14 system are also well reproduced by the model. The model invokes four-nucleon tetrahedral symmetric spatial correlations arising from three- and four-nucleon interactions, which yields a high degree of SU(4) singlet structure for the clusters and a tetrahedral intrinsic shape for the doubly magic 16O ground state. The large quadrupole moment of the 14N ground state is obtained here for the first time and arises because of the almost 100% d-wave deuteron-like-hole cluster structure inherent in the model.

Conditions for detectingCPviolation via neutrinoless double beta decay

Neutrinoless double beta decay data, together with information on the absolute neutrino masses obtained from the future KATRIN experiment and/or astrophysical measurements, provide a chance to find $CP$ violation in the lepton sector with Majorana neutrinos. We derive and discuss necessary conditions which make discovery of such $CP$ violation possible for the future neutrino oscillation and mass measurements data.

The weak production of Λ hyperons from lepton-proton scattering

We obtain the differential cross sections for the weak, strangeness changing processes, e − + p → Λ + ν e , μ − + p → Λ + ν μ , and τ − + p → Λ + ν τ as well as cross sections for the processes ν ¯ L + p → Λ + L + , where L stands for either a muon or a tau. We do this for electron energies from threshold to 2.0 GeV, for muon energies from near threshold to 5.0 GeV, for a tau energy of 20.0 GeV, and for muon antineutrino energies from threshold to 1.0 GeV and tau antineutrino energies near threshold. We discuss what might be learned from these reactions and obtain the contributions of the various form factors to these cross sections. We pay particular attention to the interference terms which may represent the only possibility of obtaining the weak magnetism form factor, F M , the pseudoscalar form factor, F P , and the form factor, F E . This latter form factor is forbidden by G-parity in the p ↔ n transition but is in principle permitted in the p ↔ Λ transition and its presence would therefore be of interest. Our calculation is a phenomenological one and makes use of SU(3) relations and Λ beta decay data.

Nuclear(μ−,e+)conversion mediated by Majorana neutrinos

We study lepton number violating (LNV) process of muon-positron conversion in nuclei mediated by the exchange of light and heavy Majorana neutrinos. Nuclear structure calculations have been carried out for the case of experimentally interesting nucleus 48Ti in the framework of renormalized proton-neutron Quasiparticle Random Phase Approximation. We demonstrate that the imaginary part of the amplitude of light Majorana neutrino exchange mechanism gives an appreciable contribution to the muon-positron conversion rate. This specific feature is absent in the allied case of neutrinoless double beta decay. Using the present neutrino oscillations, tritium beta decay, accelerator and cosmological data we derived the limits on the effective masses of light <m>_{\mu e} and heavy <M_N^{-1}>_{\mu e} neutrinos. The expected rates of muon-positron nuclear conversion, corresponding to these limits, were found to be so small that even within a distant future the muon-positron conversion experiments will hardly be able to detect the neutrino signal. Therefore, searches for this LNV process can only rely on the presence of certain physics beyond the trivial extension of the Standard Model by inclusion of massive Majorana neutrinos.

Neutrino mass in GUT constrained supersymmetry withR−parityviolation in light of neutrino oscillations

The neutrino masses are generated in grand unified theory (GUT) constrained supersymmetric model with R-parity violation. The neutrinos acquire masses via tree-level neutrino-neutralino mixing as well as via one-loop radiative corrections. The theoretical mass matrix is compared with the phenomenological one, which is reconstructed by using neutrino oscillation and neutrinoless double beta decay data. This procedure allows to obtain significantly stronger constraints on R-parity breaking parameters than those existing in the literature. The implication of normal and inverted neutrino mass hierarchy on the sneutrino expectation values, lepton-Higgs bilinear and trilinear R-parity breaking couplings is also discussed.

Solar-neutrino reactions on deuteron in effective field theory

The cross sections for low-energy neutrino–deuteron reactions are calculated within heavy-baryon chiral perturbation theory employing a cut-off regularization scheme. The transition operators are derived up to next-to-next-to-next-to-leading order in the Weinberg counting rules, while the nuclear matrix elements are evaluated using the wave functions generated by a high-quality phenomenological NN potential. With the adoption of the axial-current-four-nucleon coupling constant fixed from the tritium beta decay data, our calculation is free from unknown low-energy constants. Our results exhibit a high degree of stability against different choices of the cutoff parameter, a feature which indicates that, apart from radiative corrections, the uncertainties in the calculated cross sections are less than 1%.

On combining high and low Q2 information on the polarized parton densities

We draw attention to some problems in the combined use of high-Q^2 deep inelastic scattering (DIS) data and low-Q^2 hyperon \beta-decay data in the determination of the polarized parton densities. We explain why factorization schemes like the JET or AB schemes are the simplest in which to study the implications of the DIS parton densities for the physics of the low-Q^2 region.

Some particle physics aspects of neutrinoless double beta decay

In the analysis of double beta decay data it is usually assumed that 0νββ decay is triggered by the Majorana mass of the neutrino. However, 0νββ decay occurs in any extension of the standard model containing lepton number violation, a prominent example being supersymmetry. The amplitude of 0νββ decay in such models depends often not explicitly but only implicitly on the Majorana neutrino mass and 0νββ decay can be used to place stringent constraints on other model parameters. Here, supersymmetric contributions to 0νββ decay in both R-parity violating and R-parity conserving supersymmetry are discussed, and limits on supersymmetric parameters are derived. On the other hand, if the Majorana neutrino mass would be the dominant contribution to 0νββ decay, interesting information on the structure of the neutrino mass matrix could be obtained, once 〈 m ν 〉 is limited to be below 1 eV. A brief discussion on 〈 m ν 〉 is given in the second part of this paper.

F/D ratio in hyperon beta decays and the spin distribution in the nucleon.

It is shown that hyperon beta decay data can be well accommodated within the framework of Cabbibo's SU(3) symmetric description if one allows for a small SU(3) symmetry breaking proportional to the mass difference between strange and nonstrange quarks. The F/D ratio does not depend sensitively on the exact form of the symmetry-breaking, and the best fits are close to the value previously used in the analysis of deep inelastic scattering of electrons or muons on polarized nucleons. The total quark helicity and strange quark polarization in the nucleon are discussed.

Systematic study of beta and double beta decay to excited final states

A systematic study of the two-neutrino double beta (2νββ) decay to the final ground state and excited states is performed within an extension of the quasiparticle random-phase approximation (QRPA) model. In this extension, the multiple commutator model (MCM), a simultaneous treatment of the double-odd and double-even nuclei is possible by assuming their states to have the structure of one or two QRPA phonons. The MCM calculation is done for nine 2νβ−β− decays and six 2νECEC decays, and systematics of the relevant matrix elements and half-lives have been created. The study of the 2νββ-decay rates is complemented with the MCM study of the single-beta-decay properties of the relevant nuclei within the double-beta isobaric chains. The Woods-Saxon single-particle energies have been corrected near the Fermi surface by comparing the BCS quasiparticle energies with spectroscopic data of odd-mass nuclei. Pairing gaps, energy systematics of the Gamow-Teller states and the available beta-decay data have been used to obtain effective, model-space adapted, two-body matrix elements starting from the G-matrix elements of the Bonn one-boson-exchange potential. This enables a parameter-free calculation of the double Gamow-Teller matrix elements and theoretical prediction of double-beta half-lives.

Reanalysis of hyperon beta decay data on |F/D

We reanalyse hyperon beta decay data to extract the corresponding F and D values. We illustrate the possibility that flavour symmetry breaking effects may lead to a reduction of the F/D ratio. For proton and neutron our analyses suggests F/ D = 0.49 ± 0.08 instead of F/ D = 0.575 ± 0.016 which is generally used to analyse the spin data. Our smaller F/D value allows to fulfill the Ellis-Jaffe sum rule implying an unpolarized s s -sea.

Gamow-Teller strength in the beta + decay of 37Ca.

Calculations are presented for the Gamow-Teller strength distribution in the ${\mathrm{\ensuremath{\beta}}}^{+}$ decay of $^{37}\mathrm{Ca}$ and compared to results extracted from recent beta decay data and from (p,n) data on the analog nucleus $^{37}\mathrm{Cl}$. The strength distribution is shown to be sensitive to the Hamiltonian, and comparison with experiment indicates a need for further improvement in the 1s0d shell Hamiltonian. It also indicates that the quenching of the Gamow-Teller operator in the upper part of the 1s0d shell is similar to that deduced from previous analyses.