Beta Decay Process Research Articles

Colloquium: Majorana fermions in nuclear, particle, and solid-state physics

Ettore Majorana (1906-1938) disappeared while traveling by ship from Palermo to Naples in 1938. His fate has never been fully resolved and several articles have been written that explore the mystery itself. His demise intrigues us still today because of his seminal work, published the previous year, that established symmetric solutions to the Dirac equation that describe a fermionic particle that is its own anti-particle. This work has long had a significant impact in neutrino physics, where this fundamental question regarding the particle remains unanswered. But the formalism he developed has found many uses as there are now a number of candidate spin-1/2 neutral particles that may be truly neutral with no quantum number to distinguish them from their anti-particles. If such particles exist, they will influence many areas of nuclear and particle physics. Most notably the process of neutrinoless double beta decay can only exist if neutrinos are massive Majorana particles. Hence, many efforts to search for this process are underway. Majorana's influence doesn't stop with particle physics, however, even though that was his original consideration. The equations he derived also arise in solid state physics where they describe electronic states in materials with superconducting order. Of special interest here is the class of solutions of the Majorana equation in one and two spatial dimensions at exactly zero energy. These Majorana zero modes are endowed with some remarkable physical properties that may lead to advances in quantum computing and, in fact, there is evidence that they have been experimentally observed. This review first summarizes the basics of Majorana's theory and its implications. It then provides an overview of the rich experimental programs trying to find a fermion that is its own anti-particle in nuclear, particle, and solid state physics.

The TITAN in-trap decay spectroscopy facility at TRIUMF

This paper presents an upgraded in-trap decay spectroscopy apparatus which has been developed and constructed for use with TRIUMF׳s Ion Trap for Atomic and Nuclear science (TITAN). This device consists of an open-access electron-beam ion-trap (EBIT), which is surrounded radially by seven low-energy planar Si(Li) detectors. The environment of the EBIT allows for the detection of low-energy photons by providing backing-free storage of the radioactive ions, while guiding charged decay particles away from the trap centre via the strong (up to 6T) magnetic field. In addition to excellent ion confinement and storage, the EBIT also provides a venue for performing decay spectroscopy on highly charged radioactive ions. Recent technical advancements have been able to provide a significant increase in sensitivity for low-energy photon detection, towards the goal of measuring weak electron-capture branching ratios of the intermediate nuclei in the two-neutrino double beta (2νββ) decay process. The design, development, and commissioning of this apparatus are presented together with the main physics objectives. The future of the device and experimental technique are discussed.

Spectral structure of electron antineutrinos from nuclear reactors.

Recent measurements of the positron energy spectrum obtained from inverse beta decay interactions of reactor electron antineutrinos show an excess in the 4 to 6MeV region relative to current predictions. First-principles calculations of fission and beta decay processes within a typical pressurized water reactor core identify prominent fission daughter isotopes as a possible origin for this excess. These calculations also predict percent-level substructures in the antineutrino spectrum due to Coulomb effects in beta decay. Precise measurement of these substructures can elucidate the nuclear processes occurring within reactors. These substructures can be a systematic issue for measurements utilizing the detailed spectral shape.

Double Beta Decay Experiments: Present Status and Prospects for the Future

The review of modern experiments on search and studying of double beta decay processes is done. Results of the most sensitive current experiments are discussed. The main attention is paid to EXO-200, KamLAND-Zen, GERDA-I and CUORE-0 experiments. Modern values of T1/2(2ν) and best present limits on neutrinoless double beta decay and double beta decay with Majoron emission are presented. Conservative limits on effective mass of a Majorana neutrino (<mν> < 0.46eV) and a coupling constant of Majoron to neutrino (<gee> < 1.3 × 10−5) are obtained. In the second part of the review prospects of search for the neutrinoless double beta decay in new experiments with sensitivity to <mν> at the level of ∼ (0.01-0.1) eV are discussed. The main attention is paid to experiments of CUORE, GERDA, MAJORANA, EXO, KamLAND-Zen-2, SuperNEMO and SNO+. Possibilities of low-temperature scintillating bolometers on the basis of inorganic crystals (ZnSe, ZnMoO4, Li2MoO4, CaMoO4 and CdWO4) are considered too.

Correlation and spectrum shape measurements in β-decay probing the standard model

The beta-decay process offers unique possibilities for testing the fundamental symmetries of the standard model and searching for non-standard model components in the weak interaction. Here a non-exhaustive review of this field is given highlighting a number of key experiments or recently performed experiments. Also included are new and ongoing developments providing new opportunities for further significant progress in this research field in the era of the large hadron collider.

New Nuclear Structure and Decay Results in the 76Ge–76As System

The process of neutrinoless double beta decay (0νββ) plays a key role in modern neutrino physics. Experiments on 76Ge 0νββ-decay using germanium semiconductors are at the forefront in this field. Due to the extremely low count rates expected for this rare decay, any kind of background event in the detector, especially at energies close to Qββ=2039.006 keV must be avoided. Therefore, a careful investigation on the neutron-induced background was carried out. In this scope experiments investigating the inelastic neutron excitation of the lower lying and the 69th excited level of 76Ge have been performed. The existence of a 2040.7 keV gamma-ray, that occurs by the de-excitation of the 69th excited level, was confirmed. Interfering background from 68Ge was studied via cross-section measurements of the natGe(n,jn)68Ge reaction using quasi-monoenergetic neutrons and accelerator mass specrometry for 68Ge detection. In order to explore the matrix element for the transition between the 76Ge-76As ground states, the electron–capture of 76As has been measured for the first time.

Beta Decays and the Inner Structures of the Neutrino in a NLHV Design

A novel conceptual theory is developed for the beta decay and electron capture processes, based on the specific non-local hidden-variable (NLHV) design provided by the Cordus theory. A new mechanics is sketched out for the interactions of particules through their discrete forces, and is a deeper level representation of Feynman diagrams. The new mechanics is able to correctly predict the outcomes of the decay processes, beta minus, beta plus, electron capture. It predicts specific NLHV structures for the neutrino and antineutrino. The velocity and unique spins of the neutrino species may then be explained as a consequence of the hidden structures.

WEAK DECAY PROCESSES IN PRE-SUPERNOVA CORE EVOLUTION WITHIN THE GROSS THEORY

The beta decay and electron capture rates are of fundamental importance in the evolution of massive stars in a pre-supernova core. The beta decay process gives its contribution by emitting electrons in the plasma of the stellar core, thereby increasing pressure, which in turn increases the temperature. From the other side, the electron capture removes free electrons from the plasma of the star core contributing to the reduction of pressure and temperature. In this work we calculate the beta decay and electron capture rates in stellar conditions for 63 nuclei of relevance in the pre-supernova stage, employing Gross Theory as the nuclear model. We use the abundances calculated with the Saha equations in the hypothesis of nuclear statistical equilibrium to evaluate the time derivative of the fraction of electrons. Our results are compared with other evaluations available in the literature. They have shown to be one order less or equal than the calculated within other models. Our results indicate that these differences may influence the evolution of the star in the later stages of pre-supernova.

Searching for the Dirac Nature of Neutrinos: Combining Neutrinoless Double Beta Decay and Neutrino Mass Measurements

We studied the neutrinoless double beta decay process to tackle the issue about the nature of neutrino. Establishing the nature of neutrinos, whether they are Dirac or Majorana particles is one of the fundamental questions we need to answer in particle physics, and is related to the conservation of lepton number. Neutrinoless double beta decay ((ββ)0ν) is the tool of choice for testing the Majorana nature of neutrinos. However, up to now, this process has not been observed, but a wide experimental effort is taking place worldwide and soon new results will become available.Different mechanisms can induce (ββ)0ν-decay and might interfere with each other, potentially leading to suppressed contributions to the decay rate. This possibility would become of great interest if upcoming neutrino mass measurements from KATRIN and cosmological observations found that mν>0.2eV but no positive signal was observed in (ββ)0ν-decay experiments. We focus on the possible interference between light Majorana neutrino exchange with other mechanisms, such as heavy sterile neutrinos and R-parity violating supersymmetric models. We show that in some cases the use of different nuclei would allow to disentangle the different contributions and allow to test the hypothesis of destructive interference. Finally, we present a model in which such interference can emerge and we discuss the range of parameters which would lead to a significant suppression of the decay rate.

Radioactive contamination of BaF2crystal scintillator

Barium fluoride (BaF2) crystal scintillators are promising detectors to search for double beta decay processes in 130 Ba (Q2 = 2619(3) keV) and 132 Ba (Q2 = 844(1) keV). The 130 Ba isotope is of particular interest because of the indications on 2 decay found in two geochemical experiments. The radioactive contamination of BaF2 scintillation crystal with mass of 1.714 kg was measured over 113.4 hours in a low-background DAMA/R&D set-up deep underground (3600 m w.e.) at the Gran Sasso National Laboratories of INFN (LNGS, Italy). The half-life of 212 Po (present in the crystal scintillator due to contamination by radium) was estimated as T1/2 = 298.8 ± 0.8(stat.) ± 1.4(syst.) ns by analysis of the events pulse profiles.

Asymmetrical Genesis by Remanufacture of Antielectrons

Problem: The asymmetrical genesis problem concerns why the universe should have an abundance of matter over antimatter. Purpose: This paper shows how the baryogenesis and leptogenesis asymmetries may both be resolved. Approach: Design methods were used to develop a conceptual mechanics for the remanufacturing processes that transform particles in the decay processes. This was based on the structures for the photon, electron, antielectron, proton and antineutrino as previously identified as logical necessities for the beta decay process, and represented as a non-local hidden-variable design with discrete fields. Findings: The solution is given in terms of a mechanics that defines the transformation of discrete field structures in particles. The genesis problem is shown to be solvable. The mechanics describes pair production of an electron and antielectron from two initial photons, and subsequent remanufacture of the antielectron into a proton. It is predicted that two antineutrinos would be emitted, which are testable and falsifiable. The theory identifies that the role of the antineutrinos is to remove the antimatter handed field structures. The original electron and proton may bond to form a simple hydrogen atom, or combine via electron capture to form a neutron and hence heavier nuclides. The subsequent preponderance of the matter pathways in the genesis production sequence is also addressed and is explained as domain warfare between the matter and antimatter species. Originality: The concept of remanufacture of antielectrons into protons, with emission of antineutrinos, is novel. Extensions of the theory explain the nuclides. Consequently the theory explains from pair production up to nuclear structure, which is also original.

Decay of 161m1,m2Dy isomers under conditions of a resonance environment (Mössbauer Screen)

The half-lives of the isomers 161m1Dy and 161m2Dy (E = 25.6 keV and T 1/2 ∼ 30 ns for the former and E = 74.6 keV and T 1/2 ∼ 3 ns for the latter) placed in a 160Gd2O3 crystal lattice at T = 300 K and surrounded by stable 161Dy nuclei in the composition of 161Dy2O3 were measured by the method of (β-γ) coincidences in the beta-decay process 161Tb → 161Dy. Nuclei of 161m1,m2Dy were obtained according to the chain 160Gd(n, γ)161Gd → 161Tb → 161Dy from 160Dy2O3 weighted portions irradiated at the PWR-M reactor of the Petersburg Nuclear Physics Institute (PNPI, Gatchina, Russia). The T 1/2 value observed for the isomer 161m1Dy was found to be correlated with the number of surrounding 161Dy nuclei. The presence of this correlation in 161m1Dy can be explained by the multiple resonance scattering of photons from isomer decay within the sample used. No such correlation was observed for 161m2Dy. The half-lives measured for the isomers 161m1Dy and 161m2Dy in the absence of the above environment are 29.2(1) and 3.50(1) ns, respectively.

Ultra-low gamma-ray measurement system for neutrinoless double beta decay

An experiment for the detection of 0νβ+/EC and 0νEC/EC in 92Mo nuclei has been carried out with a scintillating crystal, CaMoO4, in coincidence with the HPGe detector. We study the background events inside the event selection window for 0ν β+/EC decays of CaMoO4 detector. For 51.2 days of data taking period, we didn't observe any event in the neutrinoless EC/EC decay event window. The 92Mo 0νβ+/EC decay half-life limit was set to 0.61×1020 years with a 90% confidence by method of Feldman and Cousins. This ultra-low gamma ray measurement utilizing coincidence technique can be used for the resonant EC/EC decay process of some nuclei which is potentially important for neutrinoless double beta decay process.

Search for2βdecays of96Ru and104Ru by ultralow-background HPGeγspectrometry at LNGS: Final results

An experiment to search for double beta decay processes in 96Ru and 104Ru, which are accompanied by gamma rays, has been realized in the underground Gran Sasso National Laboratories of the I.N.F.N. (Italy). Ruthenium samples with masses of about (0.5-0.7) kg were measured with the help of ultra-low background high purity Ge gamma ray spectrometry. After 2162 h of data taking the samples were deeply purified to reduce the internal contamination of 40K. The last part of the data has been accumulated over 5479 h. New improved half life limits on 2\beta+/\epsilon \beta+/2\epsilon\ processes in 96Ru have been established on the level of 10^{20} yr, in particular for decays to the ground state of 96Mo: T1/2(2\nu 2\beta+) > 1.4 10^{20} yr, T1/2(2\nu \epsilon\beta+) > 8.0 10^{19} yr and T1/2(0\nu 2K) > 1.0 10^{21} yr (all limits are at 90% C.L.). The resonant neutrinoless double electron captures to the 2700.2 keV and 2712.7 keV excited states of 96Mo are restricted as: T1/2(0\nu KL) > 2.0 10^{20} yr and T1/2(0\nu 2L) > 3.6 10^{20} yr, respectively. Various two neutrino and neutrinoless 2\beta\ half lives of 96Ru have been estimated in the framework of the QRPA approach. In addition, the T1/2 limit for 0\nu 2\beta- transitions of 104Ru to the first excited state of 104Pd has been set as > 6.5 10^{20} yr.

Systematic decomposition of the neutrinoless double beta decay operator

We discuss the systematic decomposition of the dimension nine neutrinoless double beta decay operator, focusing on mechanisms with potentially small contributions to neutrino mass, while being accessible at the LHC. We first provide a (d=9 tree-level) complete list of diagrams for neutrinoless double beta decay. From this list one can easily recover all previously discussed contributions to the neutrinoless double beta decay process, such as the celebrated mass mechanism or "exotics", such as contributions from left-right symmetric models, R-parity violating supersymmetry and leptoquarks. More interestingly, however, we identify a number of new possibilities which have not been discussed in the literature previously. Contact to earlier works based on a general Lorentz-invariant parametrisation of the neutrinoless double beta decay rate is made, which allows, in principle, to derive limits on all possible contributions. We furthermore discuss possible signals at the LHC for mediators leading to the short-range part of the amplitude with one specific example. The study of such contributions would gain particular importance if there were a tension between different measurements of neutrino mass such as coming from neutrinoless double beta decay and cosmology or single beta decay.

Neutrinoless double beta decay process in left-right symmetric models without scalar bidoublet

We present an alternative formulation of the left-right symmetric theory where the scalar sector consists of two Higgs doublets which differs from the standard version of the left-right model that makes use of $L-$ and $R-$ Higgs triplets and a Higgs bi-doublet. The basic idea is to consider few extra charged iso-singlet fields and the fermion masses can be realized by integrating out these heavy isosinglet fields. We also give a detailed discussion on neutrinoless double beta decay in this particular left-right symmetric theory where the right-handed Majorana neutrino can be of MeV range. With this right-handed Majorana mass around MeV scale, the contribution to neutrinoless double beta decay coming from the right-handed current can be comparable with the contributions coming from the standard left-handed sector only if the right-handed gauge boson mass is around 5 TeV, and with this operative scale of $W_R$ around few TeV, it is possible to probe at LHC. We have briefly commented on cosmological constraints coming from the big-bang nucleosynthesis and Universe cosmology to the right-handed neutrinos involved in this discussion.

Structure and symmetries of the weak interaction in nuclear beta decay

The beta decay process offers unique possibilities to search for so-called exotic, non-standard model components in the weak interaction, and for testing its fundamental symmetries. Sensitive candidates for such studies are nuclei at or close to the N = Z line for which nuclear structure-related corrections are well under control. We present here an overview of the current status of this field and discuss prospects for further significant progress in the forthcoming years.

Discovering neutrinoless double beta decay with NEXT100 detector

NEXT is a new experiment to search for neutrinoless double beta decay processes that will start operation at the LSC laboratory (Canfranc, Spain) in 2013. The apparatus is a high pressure gas xenon chamber (HPGXe) filled with 100-150 kg of gas Xenon enriched at 90% in the 136Xe isotope. NEXT proposes a novel detection technique called SOFT (Separated Optimized Function TPC) which optimizes both the energy resolution and the measurement of the topological signature of the event. This results in a powerful background rejection, which, combined with a carefully screened radiopure detector will allow NEXT to be competitive with existing proposals for next-generation neutrinoless double-beta decay experiments. First prototypes have been operating successfully in different laboratories. First results with large-scale prototypes measure a resolution of 1% FWHM at the 137Cs photopeak. This extrapolates to a resolution better than 0.5% FWHM at Qββ.

LeptonicCPviolation

Several topics on $CP$ violation in the lepton sector are reviewed. A few theoretical aspects concerning neutrino masses, leptonic mixing, and $CP$ violation will be covered, with special emphasis on seesaw models. A discussion is provided on observable effects which are manifest in the presence of $CP$ violation, particularly, in neutrino oscillations and neutrinoless double beta decay processes, and their possible implications in collider experiments such as the LHC. The role that leptonic $CP$ violation may have played in the generation of the baryon asymmetry of the Universe through the mechanism of leptogenesis is also discussed.

Contributions of the isobar analogue states to the two neutrino double beta decay process

The two neutrino double beta decay of 128, 130Te isotopes to the ground state of the 128, 130Xe isotopes has been calculated by including the contributions coming from the isobar analog states in the intermediate nuclei. The nuclear matrix elements have been computed by using the proton–neutron quasi-particle random phase approximation (pnQRPA). The broken isospin invariance of the nuclear part of the total nucleus Hamiltonian has been restored for the study of the isobar analogue excitations in the intermediate nuclei. The SU(4) symmetry violation in the shell model approximation has been considered for the investigation of the Gamow–Teller states.