Calculation Of Nuclear Matrix Elements Research Articles

Double-beta-decay nuclear matrix elements in the QRPA framework

We review the recent work done by the Jyväskylä–La Plata collaboration on the calculation of nuclear matrix elements for various modes of double-beta decays. Whenever helpful, we connect our recent work to the historical background in order to highlight the progress achieved in the field of double-beta decay. At the same time, we introduce some new concepts and ideas to treat e.g. possible backgrounds in Gamow–Teller strength functions generated in (p,n) and (n,p) reactions.

A possible probe of neutrinoless double-beta decay nuclear matrix elements

Future experiments on the search for the 0νββ decay will be sensitive to the effective Majorana mass in the region of the inverted mass hierarchy. If a positive signal is observed, a possibility to test models of calculation of nuclear matrix elements of the process will appear. We discuss this possibility in some detail.

Neutrinoless double-beta decay and seesaw mechanism

From the standard seesaw mechanism of neutrino mass generation, which is based on the assumption that the lepton number is violated at a large (~10exp(+15) GeV) scale, follows that the neutrinoless double-beta decay is ruled by the Majorana neutrino mass mechanism. Within this notion, for the inverted neutrino-mass hierarchy we derive allowed ranges of half-lives of the neutrinoless double-beta decay for nuclei of experimental interest with different sets of nuclear matrix elements. The present-day results of the calculation of the neutrinoless double-beta decay nuclear matrix elements are briefly discussed. We argue that if neutrinoless double-beta decay will be observed in future experiments sensitive to the effective Majorana mass in the inverted mass hierarchy region, a comparison of the derived ranges with measured half-lives will allow us to probe the standard seesaw mechanism assuming that future cosmological data will establish the sum of neutrino masses to be about 0.2 eV.

NEMO-3 and SuperNEMO: A search for zero neutrino double beta decay

The NEMO-3 experiment is located in the Modane Underground Laboratory (LSM) and has been taking data with seven isotopes from 2003. It is searching for the double beta decay process with two ( 2 ν β β ) or zero ( 0 ν β β ) neutrinos emitted in the final state. Precision measurements of the half-life of the isotopes due to 2 ν β β decay have been performed and updated results for all of the isotopes will be published. In particular T 1 / 2 2 ν ( Mo 100 ) = [ 7.17 ± 0.01 ( stat ) ± 0.54 ( syst ) ] ⋅ 10 18 y and the nuclear matrix elements (NME) 0.126 ± 0.006 is presented here. No evidence for 0 ν β β decay has been found and a 90% Confidence Level lower limit of T 1 / 2 0 ν ( Mo 100 ) > [ 1 ⋅ 10 24 y ] on the half-life of this process is derived. From this an upper limit can be set on the effective Majorana neutrino mass using nuclear matrix element (NME) calculations. NEMO-3 will stop in 2010. A four year R&D programme has been undertaken for SuperNEMO, the successor to NEMO-3. The construction of a demonstrator has begun and will be situated on the site of NEMO-3.

Double beta decay searches

Neutrinoless double beta decay is one of the most sensitive probes for the regime of physics beyond the standard model. It can provide fundamental information on the character of neutrinos and on their absolute mass scale. The present status of experiments searching for neutrinoless double-beta decay (ββ(0ν)) is reviewed. Given the observation of neutrino oscillations and the present knowledge of neutrino masses and mixing parameters, a possibility to observe ββ(0ν) at a neutrino mass scale in the range 10-50 meV could actually exist. This is a real challenge faced by a number of new proposed projects. The most important parameters contributing to the experimental sensitivity are outlined. A short discussion on nuclear matrix element calculations is also given.

Searching for double beta decay with the Enriched Xenon Observatory

The Enriched Xenon Observatory (EXO) will search for neutrinoless double beta decay in 136Xe. The first phase of the experiment, EXO-200, uses 200 kg of liquid xenon enriched to 80% in 136Xe in an ultra-low background time projection chamber (TPC). EXO-200 is in the final stages of assembly at the WIPP site in Carlsbad, NM and will begin taking data in 2009 with two-year sensitivity to the half-life for neutrinoless double beta decay of 6.4 × 1025 years. According to nuclear matrix element calculations, this corresponds to an effective Majorana neutrino mass of 0.13 to 0.19 eV. The EXO collaboration is also performing R&D for simultaneous detection of the decay electrons and emerging Ba ion allowing essentially background free detection in a future, ton-scale detector. The status of EXO-200 and of the ion tagging technology in liquid xenon is described.

Status of neutrinoless double beta decay searches

Neutrinoless double beta decay is one of the most sensitive tools in non-accelerator particle physics to probe the regime of physics beyond the standard model. It can provide in fact fundamental informations on the character of neutrinos and their absolute mass scale. The present status of experiments searching for neutrinoless double-beta decay (ββ(0ν)) is reviewed and the most relevant results discussed. Phenomenological aspects of ββ(0ν) are introduced. Given the observation of neutrino oscillations and the present knowledge of neutrino masses and mixing parameters, a possibility to observe ββ(0ν) at a neutrino mass scale mν in the range 10–50 meV could actually exist. The achievement of the required experimental sensitivity is a real challenge faced by a number of new proposed projects. A review of the various proposed experiments in the context of their figure-of-merit parameters is given. The most important parameters contributing to the experimental sensitivity are finally outlined. A short discussion on nuclear matrix element calculations is also given.

Nuclear matrix elements for double beta decay in the QRPA approach: A critical review

The excitement which goes with theoretical efforts towards the calculation of NME for DBD is, of course, due to the remarkable achievements of the active experimental groups. It is our pleasure and our honor to thank Profs. Ettore Fiorini and Frank Avignone for their life-long efforts devoted to the experimental exploration of DBD transitions. We wish for both of them many years of new contributions and inspirations.The calculation of nuclear matrix elements (NME) for double beta decay transitions (DBD) relies upon several approximations. The purpose of this note is to review some of these approximations, and their impact upon the NME. We shall present our results, which have been obtained in the framework of the proton-neutron quasiparticle random phase approximation (pnQRPA), and we shall focus on short range correlations, pairing, and symmetry effects.

New results for double-beta decay of 100Mo to excited final states of 100Ru using the TUNL-ITEP apparatus

The coincidence detection efficiency of the TUNL-ITEP apparatus designed for measuring half-life times of two-neutrino double-beta ( 2 ν β β ) decay transitions to excited final states in daughter nuclei has been measured with a factor of 2.4 improved accuracy. In addition, the previous measuring time of 455 days for the study of the 100Mo 2 ν β β decay to the first excited 0 1 + state in 100Ru has been increased by 450 days, and a new result (combined with the previous measurement obtained with the same apparatus) for this transition is presented: T 1 / 2 = [ 5.5 − 0.8 + 1.2 ( stat ) ± 0.3 ( syst ) ] × 10 20 yr . Measured 2 ν β β decay half-life times to excited states can be used to test the reliability of nuclear matrix element calculations needed for determining the effective neutrino mass from zero-neutrino double-beta decay data. We also present new limits for transitions to higher excited states in 100Ru which, if improved, may be of interest for more exotic conjectures, like a bosonic component to neutrino statistics.

Results from NEMO-3

The NEMO-3 experiment is located in the Modane Underground Laboratory (LSM) and has been taking data since 2003 with seven isotopes. It is searching for the double beta decay process with two (2νββ) or zero (0νββ) neutrinos emitted in the final state. Precision measurements of the half-life of the isotopes due to 2νββ decay have been performed and new results for T2ν1/2(96Zr) = [2.3 ± 0.2(stat) ± 0.3(syst)] ∣ 1019y, T2ν1/2(48Ca) = [4.4+0.5-0.4(stat) ± 0.4(syst)|·1019y and T2ν1/2(150Nd) = [0.920+0.025-0.022(stat)± 0.072 (syst)]· 1019y are presented here. Measurements of this process are important for reducing the uncertainties on the nuclear matrix elements. No evidence for 0νββ decay has been found and a 90% Confidence Level lower limit on the half-life of this process is derived. From this an upper limit can be set on the effective Majorana neutrino mass using the most recent nuclear matrix elements (NME) calculations.

Muon capture rates in Se and Cd isotopes

Energy and time spectra of γ rays following nuclear capture of negative muons in natural Se and Cd and isotopically enriched 76Se and 106Cd targets have been measured with HPGe detectors. Total muon lifetimes in Se and Cd isotopes and partial μ capture rates to excited levels of 76As and 106Ag are obtained. These results are necessary for calculation of nuclear matrix elements of the 2β decay of 76Ge and 106Cd respectively.

Double beta decay, Majorana neutrinos, and neutrino mass

The theoretical and experimental issues relevant to neutrinoless double beta decay are reviewed. The impact that a direct observation of this exotic process would have on elementary particle physics, nuclear physics, astrophysics, and cosmology is profound. Now that neutrinos are known to have mass and experiments are becoming more sensitive, even the nonobservation of neutrinoless double beta decay will be useful. If the process is actually observed, we will immediately learn much about the neutrino. The status and discovery potential of proposed experiments are reviewed in this context, with significant emphasis on proposals favored by recent panel reviews. The importance of and challenges in the calculation of nuclear matrix elements that govern the decay are considered in detail. The increasing sensitivity of experiments and improvements in nuclear theory make the future exciting for this field at the interface of nuclear and particle physics.

ββ DECAY AND NUCLEAR STRUCTURE

The determination of accurate nuclear matrix elements for ββ decay processes is a challenge for nuclear theory and can have a strong impact in neutrino physics. Large Scale Shell Model (LSSM) calculations are among the best tools for such determination and recent developments have allowed to extend its application domains. In particular, systematic studies of nuclear matrix elements calculations have been now undertaken in this framework for most of the ββ emitters. These calculations are crucial in the determination of the most favorable emitters in the forthcoming generation of ββ experiments. The present paper focuses on the recent advances and remaining difficulties of shell model calculations for the neutrinoless mode. Stability and predictive power of the results will be discussed.

Neutrinoless double-β decay: Status and future

A brief summary of the status of neutrino masses, mixing, and oscillations is presented. Neutrinoless double β decay is considered. Predictions for the effective Majorana mass are reviewed. A possible test of the calculations of nuclear matrix elements of the 0νββ decay is proposed.

Nuclear matrix elements and the neutrinoless double beta decay

Systematics of the nuclear matrix elements related to the neutrinoless double beta ( 0 ν β β ) decay are discussed. The calculation of the related nuclear matrix elements in the framework of the proton-neutron quasiparticle random-phase approximation (pnQRPA) is analyzed. In particular, the extraction of a proper value of the proton-neutron particle-particle interaction parameter in this theory is addressed. The relevance of different multipoles in the multipole decomposition of the 0 ν β β matrix element is also discussed.

Double-beta decay and neutrino mass

Recent achievements in the study of double-beta (ββ) decay are presented. We discuss the potential of this process to search, beyond Standard Model physics, for the QRPA-based methods used for the calculation of the relevant nuclear matrix elements and the derivation of the neutrino mass from both ββ-decay calculations and neutrino oscillation and cosmological data. The key position of the ββ-decay experiments in resolving the neutrino absolute mass is highlighted.

What can we learn from neutrinoless double beta decay experiments?

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 element, what is the total mass in neutrinos? 4) If neutrinoless double beta decay is observed but next generation beta decay searches for a neutrino mass only set a mass upper limit, can we establish whether the mass hierarchy is normal or inverted? We base our answers on the expected performance of next generation neutrinoless double beta decay experiments and on simulations of the accuracy of calculations of nuclear matrix elements.

Ab initio calculations of light nuclei

results from such a nucleon-based model will pro-vide a baseline against which to gauge effects of quarkand other degrees of freedom. This approach will alsoallow the accurate calculation of nuclear matrix ele-ments needed for some tests of the standard model, andof nuclei and processes not presently accessible in thelaboratory. This can be useful for astrophysical studiesand for comparisons to future radioactive beam experi-ments. To achieve this goal, we must both determine theHamiltonians to be used and devise reliable methods formany-body calculations using them. Presently, we haveto rely on phenomenological models for the nuclear in-teraction, because a quantitative understanding of thenuclear force based on quantum chromodynamics is stillfar in the future.In order to make statements about the correctness ofa given phenomenological Hamiltonian, one must beable to make calculations whose results reflect the prop-erties of the Hamiltonian and are not obscured by ap-proximations. Because the Hamiltonian is still unknown,the correctness of the calculations cannot be determinedfrom comparison with experiment. For this reason it isessential to have a number of different

The possible test of the calculations of nuclear matrix elements of the (ββ)0ν-decay

The existing calculations of the nuclear matrix elements of the neutrinoless double β-decay differ by about a factor three. This uncertainty prevents quantitative interpretation of the results of experiments searching for this process. We suggest here that the observation of the neutrinoless double β-decay of several nuclei could allow to test calculations of the nuclear matrix elements through the comparison of the ratios of the calculated lifetimes with experimental data. It is shown that the ratio of the lifetimes is very sensitive to different models.

Neutrinoless Double-Beta Decay to Excited 0+ States Mediated by Light Majorana Neutrinos

The neutrinoless double-beta decay (0νββ decay) to the first excited 0+ collective final state is examined for A = 76, 82, 100 and 136 nuclei by assuming light Majorana neutrino exchange mechanism. Realistic calculations of nuclear matrix elements are performed within the renormalized Quasiparticle Random Phase Approximation. Transitions to the first excited two-quadrupole phonon 0+ state are described within a boson expansion formalism. It is found that the 100Mo is a good candidate for experimental study of the 0νββ decay to excited 0+ state due to small suppression of this transition relative to the transition to the ground state.