The majorana neutrinoless double-beta decay experiment

The proposed Majorana double-beta decay experiment is based on an array of segmented intrinsic Ge detectors with a total mass of 500 kg of Ge isotopically enriched to 86% in ⁷⁶Ge. A discussion is given of background reduction by material selection, detector segmentation, pulse shape analysis, and electroformation of copper parts and granularity. Predictions of the experimental sensitivity are given. For an experimental running time of 10 years over the construction and operation oft he Majorana setup, a sensitivity of T _1/2 ^0ν ∼4×10²⁷ yr is predicted. This corresponds to 〈mν〉∼0.003−0.004 eV according to recent QRPA and RQRPA matrix element calculations. From Yadernaya Fizika, Vol. 67, No. 11, 2004, pp. 2025–2032. Original English Text Copyright ? 2004 by Aalseth, Anderson, Arthur, Avignone III, Baktash, Ball, Barabash, Brodzinski, Brudanin, Bugg, Champagne, Chan, Cianciolo, Collar, Creswick, Doe, Dunham, Easterday, Efremenko, Egorov, Ejiri, Elliott, Ely, Fallon, Farach, Gaitskell, Gehman, Grzywacz, Hazma, Hime, Hossbach, Jordan, Kazkaz, Kephart, King III, Kochetov, Konovalov, Kouzes, Lesko, Macchiavelli, Miley, Mills, Nomachi, Palms, Pitts, Poon, Radford, Reeves, Robertson, Rohm, Rykaczewski, Saborov, Sandukovsky, Shawley, Stekhanov, Tornow, van de Water, Vetter, Warner, Webb, Wilkerson, Wouters, Young, Yumatov. This article was submitted by the authors in English. The authors represent the Majorana Collaboration     

Chiral two-body currents in nuclei: Gamow-Teller transitions and neutrinoless double-beta decay

We show that chiral effective field theory (EFT) two-body currents provide important contributions to the quenching of low-momentum-transfer Gamow-Teller transitions, and use chiral EFT to predict the momentum-transfer dependence that is probed in neutrinoless double-beta (0νββ) decay. We then calculate for the first time the 0νββ decay operator based on chiral EFT currents and study the nuclear matrix elements at successive orders. The contributions from chiral two-body currents are significant and should be included in all calculations.     

The effect of weak magnetism and induced pseudoscalar coupling in neutrinoless double-beta decay

In calculating the amplitude of the majorana neutrino-mass mechanism of neutrinoless double-beta decay (0νββ-decay), several approximations of the nucleon current have been done. for example, effects from induced current such as weak magnetism and pseudoscalar coupling have been neglected. we shall show in this work that, although such terms do not contribute significantly to the 2νββ-decay amplitude, they are important in the case of 0νββ decay. performing calculations within the renormalized quasiparticle random phase approximation (pn-rqrpa) for all nuclei undergoing double-beta decay in the region a=76 to a=150, we have found that these additional contributions of the nucleon current reduce considerably the matrix elements in all cases for the light neutrino as well as for the heavy neutrino mass. in the light-neutrino mass, we find reductions up to thirty percent, while in the heavy-neutrino mass, up to almost a factor of five. these reductions make the limits on the lepton-number-violating parameters 〈m _ν〉 and η_N less stringent.     

Majorana neutrino masses and the neutrinoless double-beta decay

Neutrinoless double-beta decay is forbidden in the Standard Model of electroweak and strong interaction but allowed in most Grand Unified Theories (GUTs). Only if the neutrino is a Majorana particle (identical with its antiparticle) and if it has a mass is neutrinoless double-beta decay allowed. Apart from one claim that the neutrinoless double-beta decay in ⁷⁶Ge is measured, one has only upper limits for this transition probability. But even the upper limits allow one to give upper limits for the electron Majorana neutrino mass and upper limits for parameters of GUTs and the minimal R-parity-violating supersymmetric model. One further can give lower limits for the vector boson mediating mainly the right-handed weak interaction and the heavy mainly right-handed Majorana neutrino in left-right symmetric GUTs. For that, one has to assume that the specific mechanism is the leading one for neutrinoless double-beta decay and one has to be able to calculate reliably the corresponding nuclear matrix elements. In the present work, one discusses the accuracy of the present status of calculating of the nuclear matrix elements and the corresponding limits of GUTs and supersymmetric parameters. The text was submitted by the author in English.     

The neutrinoless double-beta decay: A test for new physics

The neutrinoless double-beta decay is not allowed in the Standard Model (SM) but it is allowed in most Grand Unified Theories (GUTs). The neutrino must be a Majorana particle (identical with its antiparticle) and must have a mass to allow the neutrinoless double-beta decay. Apart of one claim that the neutrinoless double-beta decay in ⁷⁶Ge is measured, one has only upper limits for this transition probability. But even the upper limits allow to give upper limits for the electron Majorana neutrino mass and upper limits for parameters of GUTs and the minimal R-parity violating supersymmetric model. One further can give lower limits for the vector boson mediating mainly the right-handed weak interaction and the heavy mainly right-handed Majorana neutrino in left-right symmetric GUTs. For that, one has to assume that the specific mechanism is the leading one for the neutrinoless double-beta decay and one has to be able to calculate reliably the corresponding nuclear matrix elements. In the present contribution, one discusses the accuracy of the present status of calculating the nuclear matrix elements and the corresponding limits of GUTs and supersymmetric parameters.     

A study of neutrinoless double-beta decay in the framework of QRPA

A study concerning the valence space dependence of neutrinoless doubleβ ⁻ decay observables is performed for several nuclei in the framework of QRPA using the multiple commutator method (MCM). Calculations and comparison to earlier results show that at least for the ground state to ground state transition the dependence is much weaker than in the two neutrino doubleβ ⁻ decay. It is still a difficult task to extract the parameters of the neutrinoless doubleβ ⁻ decay since the half-life expression contains products of the parameters 〈m _ν 〉 〈η〉 and 〈λ〉. Presented by M. Aunola at the Workshop on calculation of double-beta-decay matrix elements (MEDEX’97), Prague, May 27–31, 1997.     

Angular distribution of electrons in neutrinoless double-beta decay and new physics

For neutrinoless double-beta decay caused by the exchange of light Majorana neutrinos, an expression for the differential width with respect to the angle between the final-electron momenta is obtained on the basis of a Lorentz-invariant effective Lagrangian of the general form. The shape of this angular distribution is analyzed within various extensions of the Standard Model that allow this process—in particular, within theories that involve Majorana super partners and (or) right-handed currents. The angular correlation coefficient for electrons as a function of the mass of the right-handed W boson and the effective Majorana neutrino mass in the decay of the ⁷⁶Ge nucleus is considered within the model involving left—right symmetry.     

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

Future experiments on the search for the 0??|? 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.     

Mechanisms of neutrinoless double-beta decay: A comparative analysis of several nuclei

The neutrinoless double beta decay of several nuclei that are of interest from the experimental point of view (⁷⁶Ge, ⁸²Se, ¹⁰⁰Mo, ¹³⁰Te, and ¹³⁶Xe) is investigated on the basis of a general Lorentzinvariant effective Lagrangian describing physics effects beyond the Standard Model. The half-lives and angular-correlation coefficients for electrons are calculated for various decay mechanisms associated, in particular, with the exchange of Majorana neutrinos, supersymmetric particles (with R-parity violation), leptoquarks, and right-handed W _R bosons. The effect of theoretical uncertainties in the values of relevant nuclear matrix elements on decay features is considered.     

First results of the search for neutrinoless double-beta decay with the NEMO 3 detector

The NEMO 3 detector, which has been operating in the Fréjus underground laboratory since February 2003, is devoted to the search for neutrinoless double-beta decay (beta beta 0v). The half-lives of the two neutrino double-beta decay (beta beta 2v) have been measured for 100Mo and 82Se. After 389 effective days of data collection from February 2003 until September 2004 (phase I), no evidence for neutrinoless double-beta decay was found from approximately 7 kg of 100Mo and approximately 1 kg of 82Se. The corresponding limits are T1/2(beta beta0v) > 4.6 x 10(23) yr for 100Mo and T1/2(beta beta 0v) > 1.0 x 10(23) yr for 82Se (90% C.L.). Depending on the nuclear matrix element calculation, the limits for the effective Majorana neutrino mass are < 0.7-2.8 e/v for 100Mo and < 1.7-4.9 eV for 82Se.     

Minimal supersymmetric standard model with the gauge mediated supersymmetry breaking and the neutrinoless double-beta decay

Neutrinoless double-beta decay within Minimal Supersymmetric Standard Model with gauge mediated supersymmetry breaking is considered. Limits on R-parity breaking constant coming from non-observability of 0 in ⁷⁶Ge are found. The dependence of on different parameters at the messenger scale M are shown, with special attention paid to nuclear part of calculations. We have found that strongly depends on the effective supersymmetry breaking scale only and deduced limits imposed on this non-standard parameter by the germanium experiment.     

Effective Majorana mass and neutrinoless double beta decay

The probability distribution for the effective Majorana mass as a function of the lightest neutrino mass in the standard three neutrino scheme is computed via a random sampling from the distributions of the involved mixing angles and squared mass differences. A flat distribution in the \([0,2\pi ]\) range for the Majorana phases is assumed, and the dependence of small values of the effective mass on the Majorana phases is highlighted. The study is then extended with the addition of the cosmological bound on the sum of the neutrino masses. Finally, the prospects for \(0\nu \beta \beta \) decay search with \(^{76}\)Ge, \(^{130}\)Te and \(^{136}\)Xe are discussed, as well as those for the measurement of the electron neutrino mass.     

The effective neutrino mass of neutrinoless double-beta decays: how possible to fall into a well

The neutrinoless double-beta (\(0\nu 2\beta \)) decay is currently the only feasible process in particle and nuclear physics to probe whether massive neutrinos are the Majorana fermions. If they are of a Majorana nature and have a normal mass ordering, the effective neutrino mass term \(\langle m\rangle ^{}_{ee}\) of a \(0\nu 2\beta \) decay may suffer significant cancellations among its three components and thus sink into a decline, resulting in a “well” in the three-dimensional graph of \(|\langle m\rangle ^{}_{ee}|\) against the smallest neutrino mass \(m^{}_1\) and the relevant Majorana phase \(\rho \). We present a new and complete analytical understanding of the fine issues inside such a well, and identify a novel threshold of \(|\langle m\rangle ^{}_{ee}|\) in terms of the neutrino masses and flavor mixing angles: \(|\langle m\rangle ^{}_{ee}|^{}_* = m^{}_3 \sin ^2\theta ^{}_{13}\) in connection with \(\tan \theta ^{}_{12} = \sqrt{m^{}_1/m^{}_2}\) and \(\rho =\pi \). This threshold point, which links the local minimum and maximum of \(|\langle m\rangle ^{}_{ee}|\), can be used to signify observability or sensitivity of the future \(0\nu 2\beta \)-decay experiments. Given current neutrino oscillation data, the possibility of \(|\langle m\rangle ^{}_{ee}| < |\langle m\rangle ^{}_{ee}|^{}_*\) is found to be very small.     

Probing the mechanism of neutrinoless double beta decay with SuperNEMO

The SuperNEMO experiment is being designed to search for neutrinoless double beta decay. Its experimental technique of tracking and calorimetry provides the means to discriminate different underlying mechanisms for neutrinoless double beta decay by measuring the angular and energy distributions of electrons. The results of a study by the SuperNEMO Collaboration and F. Deppisch (in preparation) [7] for identifying light Majorana neutrino exchange and right-handed currents are presented.     

The Majorana Ge double-beta decay project

The MAJORANA Project is a research and development activity set up to establish the feasibility and cost of a double-beta decay experiment comprising a one-ton array of Ge detectors fabricated from germanium enriched to about 86% in ⁷⁶Ge.     

Testing the single-state dominance in two-neutrino double-beta decay

The single-state-dominance hypothesis (SSDH) states that the decay rates of the two-neutrino double beta decay are governed by a virtual two-step transition connecting the initial and final ground states through the first 1⁺ state, 1 ₁ ⁺ , of the intermediate odd-odd nucleus, for those odd-odd nuclei where the 1 ₁ ⁺ state is the ground state. To investigate the validity the SSDH we have performed a systematical theoretical analysis of all known double-beta-decay transitions where the SSDH conditions are fulfilled. The analysis shows that the SSDH is realized either through a true dominance of the first intermediate 1⁺ state or by cancellations among the contributions of higher lying 1⁺ states of the intermediate nucleus.