By comparing the Q-values for the 46Ti(3He,t)46V and 47Ti(3He,t)47}V reactions to the isobaric analog states the Q-value for the superallowed Fermi-decay of 46V has been determined as Q_{EC}(46V)=(7052.11+/-0.27) keV. The result is compatible with the values from two recent direct mass measurements but is at variance with the previously most precise reaction Q-value. As additional input quantity we have determined the neutron separation energy S_n(47Ti)=(8880.51+/-0.25) keV.
Spectroscopic studies of two beta-rays from 100Mo are shown to be of potential interest for investigating both the Majorana neutrino mass by neutrinoless double beta-decay and low energy solar neutrino's by inverse beta-decay. With a multi-ton 100Mo detector, coincidence studies of correlated beta-beta from neutrinoless double beta-decay, together with the large Q value, permit identification of the neutrino-mass term with a sensitivity of ~ 0.03 eV. Correlation studies of the inverse beta and the successive beta-decay of 100Tc, together with the large capture rates for low energy solar neutri…
Possibilities to search for double beta decay of alpha/beta unstable nuclei, many of which have higher energy release than "conventional" (beta stable) double beta decay candidates, are discussed. First experimental half-life limits on double beta decay of radioactive nuclides from U and Th families (trace contaminants of the CaWO_4, CdWO_4 and Gd_2SiO_5 scintillators) were established by reanalyzing the data of low-background measurements in the Solotvina Underground Laboratory with these detectors (1734 h with CaWO_4, 13316 h with CdWO_4, and 13949 h with Gd_2SiO_5 crystals).
Electromagnetic transitions from isobaric analogue states to study nuclear matrix elements for double beta decays and astro-neutrino inverse beta decays
We present for the first time precise spectroscopic information on the recently discovered decay mode beta-delayed 3p-emission. The detection of the 3p events gives an increased sensitivity to the high energy part of the Gamow-Teller strength distribution from the decay of 31Ar revealing that as much as 30% of the strength resides in the beta-3p decay mode. A simplified description of how the main decay modes evolve as the excitation energy increases in 31Cl is provided.
Active background reduction in high resolution calorimeters is a promising approach to achieve ultimate sensitivity in neutrinoless double beta decay experiments. We propose Cerenkov emission from beta rays in bolometric crystals as a viable alternative to scintillation. This novel approach could broaden the range of materials of interest for calorimetric searches of the double beta decay. We discuss the optical properties of TeO$_2$ crystals, as a show case.
Neutrinoless double beta decay is one of the most powerful tools to set the neutrino mass absolute scale and establish whether the neutrino is a Majorana particle. After a summary of the neutrinoless double beta decay phenomenology, the present status of the experimental search for this rare decay is reported and the prospects for next generation experiments are reviewed.
At least one neutrino has a mass of about 50 meV or larger. However, the absolute mass scale for the neutrino remains unknown. Studies of double beta decay offer hope for determining the absolute mass scale. Furthermore, the critical question: Is the neutrino its own antiparticle? is unanswered. In particular, zero-neutrino double beta decay can address the issues of lepton number conservation, the particle-antiparticle nature of the neutrino, and its mass. A summary of the recent progress in double beta decay, and the related technologies will be discussed in the context of the future double …
Main achievements during 75 years of research on double beta decay have been reviewed. The existing experimental data have been presented and the capabilities of the next-generation detectors have been demonstrated.
The present status of double beta decay experiments is reviewed. The results of the most sensitive experiments are discussed. Proposals for future double beta decay experiments with a sensitivity to the $< m_ν >$ at the level of (0.01--0.1) eV are considered.
In the field of Double Beta Decay (DBD) searches, the use of high resolution detectors in which background can be actively discriminated is very appealing. Scintillating bolometers containing a Double Beta Decay emitter can largely fulfill this very interesting possibility. In this paper we present the latest results obtained with CdWO4 and CaMoO4 crystals. Moreover we report, for the first time, a very interesting feature of CaMoO4 bolometers: the possibility to discriminate beta-gamma events from those induced by alpha particles thanks to different thermal pulse shape.
The brief review of current experiments on search and studying of double beta decay processes is done. Best present limits on $\langle m_ν \rangle$ and $\langle g_{ee} \rangle$ are presented. Prospects of search for neutrinoless double beta decay in new experiments with sensitivity to $\langle m_ν\rangle$ at the level of $\sim$ 0.01-0.1 eV are discussed.
Detector DEVIS is TPC in the magnetic field. It is dedicated to the investigation of the double-beta decay of Xe. Setup sensitivity was estimated in the series of measurements with Xe with natural isotopes composition. Detector allows measuring two-neutrino double-beta decay of $^{136}$Xe with half-life less than $3 \cdot 10^{20}$ years.
A brief review on double beta decay to excited states of daughter nuclei is given. The ECEC(ov) transision to the excited states are discussed in association with a possible enhancement of the decay rate by several orders of magnitude.
In an experiment performed at the LISE3 facility of GANIL, we studied the decay of 22Al produced by the fragmentation of a 36Ar primary beam. A beta-decay half-life of 91.1 +- 0.5 ms was measured. The beta-delayed one- and two-proton emission as well as beta-alpha and beta-delayed gamma decays were measured and allowed us to establish a partial decay scheme for this nucleus. New levels were determined in the daughter nucleus 22Mg. The comparison with model calculations strongly favours a spin-parity of 4+ for the ground state of 22Al.
Energy resolution, alpha/beta ratio, pulse-shape discrimination for gamma rays and alpha particles, radioactive contamination were studied with neodymium doped yttrium-aluminum garnet (YAG:Nd). Applicability of YAG:Nd scintillators to search for double beta decay and alpha activity of natural neodymium isotopes are discussed.
The double beta decay study of 160-Gd has been performed in the Solotvina Underground Laboratory with the help of Gd_2SiO_5(Ce) crystal scintillator (volume 95 cc). The background of the detector in the vicinity of the 2 beta energy of 160-Gd was reduced to 1.0 cpd/keV kg. The new improved half-life limits have been established for neutrinoless 2 beta decay of 160-Gd to the ground and first excited levels of 160-Dy: T1/2 > 2.3(1.3)E21 yr at 68%(90%) C.L. The T1/2 bounds have been also set for two neutrino mode as well as for 2 beta decay with Majorons emission. Also the limits were established…
The document presents a summary of discussions at recent workshops at the Amherst Center for Fundamental Interactions at Amherst, MA, and at the European Centre for Theoretical Studies in Nuclear Physics and Related Areas at Trento, Italy, on the potential sensitivity of precision beta-decay experiments towards new physics.
Measurements of the beta decay correlation coefficients in nuclear decay aim for a precision below $1\%$ and theoretical predictions should follow this trend. In this work, the influence of the two dominant Standard Model correction terms, i.e. the recoil-order and the radiative correction, are studied for the most commonly measured beta correlations, i.e. the $β$-asymmetry parameter ($A_β$) and the $β-ν$ angular correlation ($a_{βν}$). The recoil-order correction is calculated with the well-known Holstein formalism using the impulse approximation to evaluate experimentally inaccessible form f…
Precision measurements in free neutron beta decay serve to determine the coupling constants of beta decay, and offer several stringent tests of the Standard Model. This paper describes the free neutron beta decay program planned for the Fundamental Physics Beamline at the Spallation Neutron Source at Oak Ridge National Laboratory, and puts it into the context of other recent and planned measurements of neutron beta decay observables.
The $^{11}$Be neutron halo nucleus appears to decay into $^{10}$Be with a rate that exceeds expectations. Neutron disappearance into dark matter, beta decay of a halo neutron, or beta-delayed proton decay have been offered as explanations. In this work we study the latter option; we carry out shell model calculations and sequential decay analysis examining the beta-delayed proton decay going through a resonance in $^{11}$B. The narrow energy window, lack of states with sufficient spectroscopic strength, overwhelming alpha decay branch, all make reconciling the observed rate with beta-delayed p…
The beta-strength in beta-delayed particle decays has up to now been defined in a somewhat ad hoc manner that depends on the decay mechanism. A simple, consistent definition is presented that fulfils the beta strength sum rules. Special consideration is given to the modifications needed when employing R-matrix fits to data. As an example the 11Be(beta-p) decay is investigated through simple models.
A collection of stories is presented on discoveries of double beta decay (including neutrinoless one) which were refuted in the subsequent investigations.
Nuclear matrix elements (NMEs) for two neutrino double beta decays are discussed in terms of the Fermi Surface Quasi-Particle (FSQP) Model. The evaluated NMEs agree with the observed NMEs . The new NMEs for two neutrino double beta decays from Kr78, Cd106, Ba130, and Pd110 were evaluated by FSQP. The NMEs show shell configuration dependence. Impacts of the FSQP NMEs for two neutrino double beta decays on the NMEs for neutrino less double beta decays are discussed.
Crystal scintillators are very promising detectors to investigate double beta decay of atomic nuclei. Recent achievements in development and application of tungstate and molybdate crystal scintillators as well as prospects for the next generation double beta decay experiments are discussed.
With more intense sources of cold and ultracold neutrons becoming available and with improved experimental techniques being developed, determination of |Vud| from neutron beta decay with a similar precision to that from from superallowed beta decays is within reach. Determination of |Vud| from neutron beta decay, free from nuclear corrections, hold the most promise for a further improvement of the determination of |Vud|. The current and future neutron beta decay correlation experiments including the UCNA experiment at Los Alamos National Laboratory are reviewed
Beta-decay into broad resonances gives a distorted lineshape in the observed energy spectrum. Part of the distortion arises from the phase space factor, but we show that the beta-decay matrix element may also contribute. Based on a schematic model for p-wave continuum neutron states it is argued that beta-decay directly to the continuum should be considered as a possible contributing mechanism in many decays close to the driplines. The signatures in R-matrix fits for such decays directly to continuum states are discussed and illustrated through an analysis of the beta-decay of $^8$B into $2^+$…
The current situation in double beta decay experiments , the characteristics of modern detectors and the possibility of increasing the sensitivity to neutrino mass in future experiments are discussed. The issue of the production and use of enriched isotopes in double beta decay experiments is discussed in addition.
Current status of experimental investigations of rare single beta decays (48Ca, 50V, 96Zr, 113Cd, 113mCd, 115In, 123Te, 180mTa, 222Rn) is reviewed. Nuclei which decay through single beta decay very often constitute backgrounds in studies of rare effects like double beta decay, solar neutrinos or dark matter. Summary of correction factors used in description of forbidden beta decays is also briefly given.
Neutrinoless Double Beta Decay is a hypothesised nuclear process in which two neutrons simultaneously decay into protons with no neutrino emission. The prized observation of this decay would point to the existence of a process that violates a fundamental symmetry of the Standard Model of Particle Physics, and would allow to establish the nature of neutrinos. Today, the lower limits on the half-life of this process exceed 10$^{25}$-10$^{26}$ yr. I will review the current status of the searches for Double Beta Decay and the perspectives to enhance the experimental sensitivity in the next years.
Neutrinoless double beta decay is a lepton number violating process whose observation would also establish that neutrinos are their own anti-particles. There are many experimental efforts with a variety of techniques. Some (EXO, Kamland-Zen, GERDA phase I and CANDLES) started take data in 2011 and EXO has reported the first measurement of the half life for the double beta decay with two neutrinos of $^{136}$Xe. The sensitivities of the different proposals are reviewed.
The search for neutrino-less double-beta decay has been a very active field of research in the last decade. Neutrino-less double-beta decay may answer essential open questions in neutrino physics. While double-beta decay accompanied by the emission of two neutrinos is allowed by the Standard Model, the neutrino-less process requires neutrinos to be Majorana particles. Detecting this decay could determine the nature of neutrinos, the neutrino effective mass, and the mass hierarchy. Xenon-136 and germanium-76 experiments currently have the best sensitivities. For both isotopes the lifetime of ne…
It is shown that differences, due to charge-dependent effects, in the 17N and 17Ne ground-state wave functions account for the fact that the experimentally measured branch for the beta+ decay of 17Ne to the first excited state of 17F is roughly a factor of two larger than expected on the basis of nuclear matrix elements which reproduce the corresponding beta- branch in the decay of 17N.
The search for neutrinoless double beta decay is a rich source for new physics. The observation of this decay will lead to understanding of the absolute mass scale of neutrinos, the Majorana nature of the neutrino (whether the neutrino is its own anti-particle), and lepton number violation. Double beta decay is being investigated around the world by several experiments using different candidate isotopes. There has been much progress made in experimental techniques recently such that achieving sensitivity to neutrino masses at 50 meV and below will be possible in the near future. A summary of r…
The exact relativistic form for the beta decay endpoint spectrum is derived and presented in a simple factorized form. We show that our exact formula can be well approximated to yield the endpoint form used in the fit method of the KATRIN collaboration. We also discuss the three neutrino case and how information from neutrino oscillation experiments may be useful in analyzing future beta decay endpoint experiments.
An earlier publication "The implication of the atomic effects in neutrinoless double beta (0$νββ$) decay" written by Mei and Wei has motivated us to compare the decay Q value ($Q_{ββ}$) derived from the decay of the parent nucleus to the daughter nucleus with the two ejected beta particles in the final state to the $Q_{ββ}$ directly derived from the decay of the initial neutral atom to the final state of double-ionized daughter ion with the two ejected beta particles in the final state. We show that the results are the same, which is the mass-energy difference ($ΔMc^2$) subtracted by the total…
In anticipation of results from current and future double-beta decay studies, we report a measurement resulting in a 82Se double-beta decay Q-value of 2997.9(3) keV, an order of magnitude more precise than the currently accepted value. We also present preliminary results of a calculation of the 82Se neutrinoless double-beta decay nuclear matrix element that corrects in part for the small size of the shell model single-particle space. The results of this work are important for designing next generation double-beta decay experiments and for the theoretical interpretations of their observations.
Neutrinoless double beta decays in liquid xenon produce a significant amount of Cherenkov light, with a photon number and angular distribution that distinguishes these events from common backgrounds. A GEANT4 simulation was used to simulate Cherenkov photon production and measurement in a liquid xenon detector and a multilayer perceptron was used to analyze the resulting distributions to classify events based on their Cherenkov photons. Our results show that a modest improvement in the sensitivity of neutrinoless double beta decay searches is possible using this technique, but the kinematics o…
Xenon time projection chambers (TPCs) have become a well-established detection technology for neutrinoless double beta decay searches in $^{136}$Xe. I discuss the motivations for this choice. I describe the status and prospects of both liquid and gaseous xenon TPC projects for double beta decay.
Limits on parameters describing physics beyond the Standard Model are presented. The most general Lorentz invariant effective Hamiltonian at the quark-lepton level involving vector, scalar and tensor operators has been used. The fits have been done using the most precise and up to date experimental data for correlation coefficients measured in free neutron beta decay as well as the Fierz term measured in superallowed Fermi decays.
We investigate several Pb$(n,n'γ$) and Ge$(n,n'γ$) reactions. We measure $γ$-ray production from Pb$(n,n'γ$) reactions that can be a significant background for double-beta decay experiments which use lead as a massive inner shield. Particularly worrisome for Ge-based double-beta decay experiments are the 2041-keV and 3062-keV $γ$ rays produced via Pb$(n,n'γ$). The former is very close to the ^{76}Ge double-beta decay endpoint energy and the latter has a double escape peak energy near the endpoint. Excitation $γ$-ray lines from Ge$(n,n'γ$) reactions are also observed. We consider the contributi…
We assess how well next generation neutrinoless double beta decay and normal neutrino beta decay experiments can answer four fundamental questions. 1) If neutrinoless double beta decay searches do not detect a signal, and if the spectrum is known to be inverted hierarchy, can we conclude that neutrinos are Dirac particles? 2) If neutrinoless double beta decay searches are negative and a next generation ordinary beta decay experiment detects the neutrino mass scale, can we conclude that neutrinos are Dirac particles? 3) If neutrinoless double beta decay is observed with a large neutrino mass el…
The nuclear matrix element for the two neutrino double beta decay (DBD) of 136Xe was evaluated by FSQP (Fermi Surface Quasi Particle model), where experimental GT strengths measured by the charge exchange reaction and those by the beta decay rates were used. The 2 neutrino DBD matrix element is given by the sum of products of the single beta matrix elements via low-lying (Fermi Surface) quasi-particle states in the intermediate nucleus. 136Xe is the semi-magic nucleus with the closed neutron-shell, and the beta + transitions are almost blocked. Thus the 2 neutrino DBD is much suppressed. The e…
The potential of large scale Yb-loaded liquid scintillators as proposed for solar neutrino spectroscopy are investigated with respect to double beta decay. The potential for beta-beta- - decay of 176Yb as well as the beta+/EC - decay for 168Yb is discussed. Not only getting for the first time an experimental half-life limit on 176Yb - decay, this will even be at least comparable or better than existing ones from other isotopes. Also for the first time a realistic chance to detect beta+/EC - decay exists. Effects of MeV-neutrinos are discussed as well.
Low-energy experiments studying single beta decay can serve as sensitive probes of Lorentz invariance that can complement interferometric searches for deviations from this spacetime symmetry. Experimental signatures of a dimension-three operator for Lorentz violation that are unobservable in neutrino oscillations are described for the decay the polarized and unpolarized neutrons as well as for measurements of the spectral endpoint in beta decay.
The physics potential of neutrinoless double beta decay is discussed. Furthermore, experimental considerations are presented as well as the current status of experiments. Finally an outlook towards the future, work on nuclear matrix elements and alternative processes is given.
In the minimal supersymmetric extension to the Standard Model, a non-zero lepton number violating coupling lambda'_111 predicts both neutrinoless double beta decay and resonant single slepton production at the LHC. We show that, in this case, if neutrinoless double beta decay is discovered in the next generation of experiments, there exist good prospects to observe single slepton production at the LHC. Neutrinoless double beta decay could otherwise result from a different source (such as a non-zero Majorana neutrino mass). Resonant single slepton production at the LHC can therefore discriminat…
We study in this letter the double beta decay of 136Xe with emission of two neutrinos which has been recently measured by the EXO-200 collaboration. We use the same shell model framework, valence space, and effective interaction that we have already employed in our calculation of the nuclear matrix element (NME) of its neutrinoless double beta decay. Using the quenching factor of the Gamow-Teller operator which is needed to reproduce the very recent high resolution 136Xe (3He, t)136Cs data, we obtain a nuclear matrix element M(2nu)=0.025 MeV^(-1) compared with the experimental value M(2nu)=0.0…
We propose to use charged-current neutrino-nucleus interactions as a probe of the many virtual transitions involved in neutrinoless double-beta decay. By performing neutrino and anti-neutrino interaction studies on the initial and final nucleus respectively, one can get information on the two branches involved in the double-beta decay process. The measurement of such reactions could help to further constrain double-beta decay predictions on the half-lives.
We calculate the bound-state beta^- decay rate of the free neutron. We show that hydrogen in the final state of the decay is produced with a probability of about 99% in the hyperfine state with zero orbital l = 0 and atomic angular momentum F = 0.
We review recent developments in double-beta decay, focusing on what can be learned about the three light neutrinos in future experiments. We examine the effects of uncertainties in already measured neutrino parameters and in calculated nuclear matrix elements on the interpretation of upcoming double-beta decay measurements. We then review a number of proposed experiments.
The interest, the status and the perspectives of various experiments in neutron and nuclear beta-decay, muon-decay and pion-decays are discussed. The talk is segmented into a discussion of the decay-rates and of the energy-spectra and correlations. The impact on various scenarios of "new physics" is briefly mentioned; left-right symmetric models are discussed in more detail and the informations gained from the considered experiments is compared to those from other sources.
We analyse the sensitivity of all experimentally observable asymmetries and energy distributions for the neutron beta-decay with a polarised neutron and unpolarised decay proton and electron and the lifetime of the neutron to contributions of order 10^(-4) of interactions beyond the Standard model (SM).
Of the many extensions to the standard model that could possibly generate neutrino mass, most necessitate the neutrino being a Majorana fermion. If this is the case, the rare process of neutrinoless double beta decay is predicted with half lives greater than about $10^{25}$ years. Many current and future experiments look for this decay by identifying a summed double beta energy at the Q value of the decay, but adding energy and angular measurements of the individual betas allows the underlying decay mechanism to be probed. A novel nano-tracking detector based on a clever combination of thin fi…
Deviations from Lorentz and CPT invariance in the neutrino sector and their observable effects in double beta decay are studied. For two-neutrino double beta decay, a spectral distortion and its properties are characterized for different isotopes. Majorana couplings for Lorentz violation are studied and shown to trigger neutrinoless double beta decay even for negligible Majorana mass. Existing data are used to obtain first limits of $5 \times 10^{-9}$ for 18 individual coefficients and attainable sensitivities in current and future experiments are presented.
