The direction of individual $^8$B solar neutrinos has been reconstructed using the SNO+ liquid scintillator detector. Prompt, directional Cherenkov light was separated from the slower, isotropic scintillation light using time information, and a maximum likelihood method was used to reconstruct the direction of individual scattered electrons. A clear directional signal was observed, correlated with the solar angle. The observation was aided by a period of low primary fluor concentration that resulted in a slower scintillator decay time. This is the first time that event-by-event direction reconstruction in high light-yield liquid scintillator has been demonstrated in a large-scale detector.

HAL is a multi-disciplinary open access archive for the deposit and dissemination of scientific research documents, whether they are published or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers. L’archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d’enseignement et de recherche français ou étrangers, des laboratoires publics ou privés. Limits on different Majoron decay modes of Mo and Se for neutrinoless double beta decays in the NEMO-3 experiment R. Arnold, C. Augier, J. Baker, A.S. Barabash, V. Brudanin, A.J. Caffrey, E. Caurier, V. Egorov, K. Errahmane, A.I. Etienvre, et al.

We have constructed a GEANT4-based detailed software model of photon transport in plastic scintillator blocks and have used it to study the NEMO-3 and SuperNEMO calorimeters employed in experiments designed to search for neutrinoless double beta decay. We compare our simulations to measurements using conversion electrons from a calibration source of 207Bi and show that the agreement is improved if wavelength-dependent properties of the calorimeter are taken into account. In this article, we briefly describe our modeling approach and results of our studies.

We report results from the NEMO-3 experiment based on an exposure of 1275 days with 661 g of (130)Te in the form of enriched and natural tellurium foils. The ββ decay rate of (130)Te is found to be greater than zero with a significance of 7.7 standard deviations and the half-life is measured to be T(½)(2ν) = [7.0 ± 0.9(stat) ± 1.1(syst)] × 10(20) yr. This represents the most precise measurement of this half-life yet published and the first real-time observation of this decay.

We report results from the NEMO-3 experiment based on an exposure of 1275 days with 661 g of (130)Te in the form of enriched and natural tellurium foils. The ββ decay rate of (130)Te is found to be greater than zero with a significance of 7.7 standard deviations and the half-life is measured to be T(½)(2ν) = [7.0 ± 0.9(stat) ± 1.1(syst)] × 10(20) yr. This represents the most precise measurement of this half-life yet published and the first real-time observation of this decay.

We report results from the NEMO-3 experiment based on an exposure of 1275 days with 661 g of Te-130 in the form of enriched and natural tellurium foils. The beta beta decay rate of Te-130 is found to be greater than zero with a significance of 7.7 standard deviations and the half-life is measured to be T-1/2(2v)=[7.0 +/- 0.9(stat) +/- 1: 1(syst)] x 10(20) yr. This represents the most precise measurement of this half- life yet published and the first real-time observation of this decay.

Using 9.4 g of Zr-96 and 1221 days of data from the NEMO-3 detector corresponding to 0.031 kg yr, the obtained 2vbb decay half-life measurement is [2.35 +/- 0.14(stat) +/- 0.16(syst)] x 10^19 yr. Different characteristics of the final state electrons have been studied, such as the energy sum, individual electron energy, and angular distribution. The 2v nuclear matrix element is extracted using the measured 2vbb half-life and is 0.049 +/- 0.002. Constraints on 0vbb decay have also been set.

The possibility to probe new physics scenarios of light Majorana neutrino exchange and right-handed currents at the planned next generation neutrinoless double beta decay experiment SuperNEMO is discussed. Its ability to study different isotopes and track the outgoing electrons provides the means to discriminate different underlying mechanisms for the neutrinoless double beta decay by measuring the decay half-life and the electron angular and energy distributions.

The development of BiPo detectors is dedicated to the measurement of extremely high radiopurity in 208Tl and 214Bi for the SuperNEMO double beta decay source foils. A modular prototype, called BiPo-1, with 0.8 m2 of sensitive surface area, has been running in the Modane Underground Laboratory since February, 2008. The goal of BiPo-1 is to measure the different components of the background and in particular the surface radiopurity of the plastic scintillators that make up the detector. The first phase of data collection has been dedicated to the measurement of the radiopurity in 208Tl. After more than one year of background measurement, a surface activity of the scintillators of A(Tl208)=1.5μBq/m2 is reported here. Given this level of background, a larger BiPo detector having 12 m2 of active surface area, is able to qualify the radiopurity of the SuperNEMO selenium double beta decay foils with the required sensitivity of A(Tl208)<2μBq/kg (90% C.L.) with a six month measurement.

J. Argyriades,1 R. Arnold,2 C. Augier,1 J. Baker,3 A. S. Barabash,4 A. Basharina-Freshville,5 M. Bongrand,1 G. Broudin,6,7 V. Brudanin,8 A. J. Caffrey,3 E. Chauveau,6,7 Z. Daraktchieva,5 D. Durand,9 V. Egorov,8 N. Fatemi-Ghomi,10 R. Flack,5 Ph. Hubert,6,7 J. Jerie,13 S. Jullian,1 M. Kauer,5 S. King,5 A. Klimenko,8 O. Kochetov,8 S. I. Konovalov,4 V. Kovalenko,8 D. Lalanne,1 T. Lamhamdi,11 K. Lang,12 Y. Lemière,9 C. Longuemare,9 G. Lutter,6,7 Ch. Marquet,6,7 J. Martin-Albo,14 F. Mauger,9 A. Nachab,6,7 I. Nasteva,10 I. Nemchenok,8 F. Nova,15 P. Novella,14 H. Ohsumi,16 R. B. Pahlka,12 F. Perrot,6,7 F. Piquemal,6,7 J. L. Reyss,17 J. S. Ricol,6,7 R. Saakyan,5 X. Sarazin,1 L. Simard,1 F. Šimkovic,18 Yu. Shitov,8 A. Smolnikov,8 S. Snow,10 S. Söldner-Rembold,10 I. Štekl,13 J. Suhonen,19 C. S. Sutton,20 G. Szklarz,1 J. Thomas,5 V. Timkin,8 V. Tretyak,8 V. Umatov,4 L. Vála,13 I. Vanyushin,4 V. Vasiliev,5 V. Vorobel,21 and Ts. Vylov8 (NEMO Collaboration) 1LAL, Université Paris-Sud 11, CNRS/IN2P3, Orsay, France 2IPHC, Université de Strasbourg, CNRS/IN2P3, F-67037 Strasbourg, France 3INL, Idaho Falls, Idaho 83415, USA 4Institute of Theoretical and Experimental Physics, RU-117259 Moscow, Russia 5University College London, WC1E 6BT London, United Kingdom 6Université de Bordeaux, Centre d’Etudes Nucléaires de Bordeaux Gradignan, UMR 5797, F-33175 Gradignan, France 7CNRS/IN2P3, Centre d’Etudes Nucléaires de Bordeaux Gradignan, UMR 5797, F-33175 Gradignan, France 8Joint Institute for Nuclear Research, RU-141980 Dubna, Russia 9LPC Caen, ENSICAEN, Université de Caen, Caen, France 10University of Manchester, M13 9PL Manchester, United Kingdom 11USMBA, Fes, Morocco 12University of Texas at Austin, Austin, Texas 78712-0264, USA 13IEAP, Czech Technical University in Prague, CZ-12800 Prague, Czech Republic 14IFIC, CSIC – Universidad de Valencia, Valencia, Spain 15Universitat Autònoma de Barcelona, Spain 16Saga University, Saga 840-8502, Japan 17LSCE, CNRS, F-91190 Gif-sur-Yvette, France 18FMFI, Comenius University, SK-842 48 Bratislava, Slovakia 19Jyväskylä University, FIN-40351 Jyväskylä, Finland 20MHC, South Hadley, Massachusetts 01075, USA 21Charles University, Prague, Czech Republic

The half-life for double-{beta} decay of {sup 150}Nd has been measured by the NEMO-3 experiment at the Modane Underground Laboratory. Using 924.7 days of data recorded with 36.55 g of {sup 150}Nd, we measured the half-life for 2{nu}{beta}{beta} decay to be T{sub 1/2}{sup 2{nu}}=(9.11{sub -0.22}{sup +0.25}(stat.){+-}0.63(syst.))x10{sup 18} yr. The observed limit on the half-life for neutrinoless double-{beta} decay is found to be T{sub 1/2}{sup 0{nu}}>1.8x10{sup 22} yr at 90% confidence level. This translates into a limit on the effective Majorana neutrino mass of <4.0-6.3 eV if the nuclear deformation is taken into account. We also set limits on models involving Majoron emission, right-handed currents, and transitions to excited states.

In the double beta decay experiment NEMO 3 a precise knowledge of the background in the signal region is of outstanding importance. This article presents the methods used in NEMO 3 to evaluate the backgrounds resulting from most if not all possible origins. It also illustrates the power of the combined tracking-calorimetry technique used in the experiment.

The double beta decay of 100Mo to the 01 and 2 + 1 excited states of 100Ru is studied using the NEMO 3 data. After the analysis of 8024 h of data the half-life for the two-neutrino double beta decay of 100Mo to the excited 01 state is measured to be T (2ν) 1/2 = [5.7 +1.3 −0.9(stat)±0.8(syst)]·10 y. The signal-to-background ratio is equal to 3. Information about energy and angular distributions of emitted electrons is also obtained. No evidence for neutrinoless double beta decay to the excited 01 state has been found. The corresponding half-life limit is T (0ν) 1/2 (0 + → 01 ) > 8.9 · 1022 y (at 90% C.L.). The search for the double beta decay to the 21 excited state has allowed the determination of limits on the half-life for the two neutrino mode T (2ν) 1/2 (0 + → 21 ) > 1.1·1021 y (at 90% C.L.) and for the neutrinoless mode T (0ν) 1/2 (0+ → 2 + 1 ) > 1.6·1023 y (at 90% C.L.).

The NEMO-3 tracking detector is located in the Fréjus Underground Laboratory. It was designed to study double beta decay in a number of different isotopes. Presented here are the experimental half-life limits on the double beta decay process for the isotopes 100Mo and 82Se for different majoron emission modes and limits on the effective neutrino–majoron coupling constants. In particular, new limits on “ordinary” majoron (spectral index 1) decay of 100Mo (T1/2>2.7×1022yr) and 82Se (T1/2>1.5×1022yr) have been obtained. Corresponding bounds on the majoron–neutrino coupling constant are 〈gee〉<(0.4–1.8)×10−4 and <(0.66–1.9)×10−4.

The development of the NEMO3 detector, which is now running in the Frejus Underground Laboratory (L.S.M. Laboratoire Souterrain de Modane), was begun more than ten years ago. The NEMO3 detector uses a tracking-calorimeter technique in order to investigate double beta decay processes for several isotopes. The technical description of the detector is followed by the presentation of its performance.

After analysis of 5797 h of data from the detector NEMO3, new limits on neutrinoless double beta decay of 100Mo (T1/2>3.1×1023y, 90% CL) and 82Se (T1/2>1.4×1023y, 90% CL) have been obtained. The corresponding limits on the effective majorana neutrino mass are: 〈mv〉<(0.8–1.2) eV and 〈mv〉<(1.5–3.1) eV, respectively. Also the limits on double-beta decay with Majoron emission are: T1/2>1.4×1022y (90% CL) for 100Mo and T1/2>1.2×1022y (90% CL) for 82Se. Corresponding bounds on the Majoron-neutrino coupling constant are 〈 gee〉<(0.5–0.9)×10−4 and <(0.7−1.6)×10−4. Two-neutrino 2β-decay half-lives have been measured with a high accuracy, \(T_{1/2}^{100_{Mo} } = [7.68 \pm 0.02(stat) \pm 0.54(syst)] \times 10^{18} y\) and \(T_{1/2}^{82_{Se} } = [10.3 \pm 0.3(stat) \pm 0.7(syst)] \times 10^{19} y\).

After analysis of 5797 h of data from the detector NEMO3, new limits on neutrinoless double beta decay of (100)Mo (T(1/2) > 3.1 x 10(23) y, 90% CL) and (82)Se (T(1/2) > 1.4 x 10(23) y, 90% CL) have been obtained. The corresponding limits on the effective majorana neutrino mass are: < (0.8-1.2) eV and < (1.5-3.1) eV, respectively. Also the limits on double-beta decay with Majoron emission are: T(1/2) > 1.4 x 10(22) y (90% CL) for (100)Mo and T(1/2) > 1.2 x 10(22) y (90% CL) for (82)Se. Corresponding bounds on the Majoron-neutrino coupling constant are < (0.5-0.9) x 10(- 4) and <(0.7-1.6) x 10(- 4). Two-neutrino 2beta-decay half-lives have been measured with a high accuracy, T(1/2)(100)Mo = [7.68 +/- 0.02(stat) +/- 0.54(syst)] x 10(18) y and T(1/2)(82)Se = [10.3 +/- 0.3(stat) +/- 0.7(syst)] x 10(19) y. (C) 2004 MAIK "Nauka/Interperiodica".

The background induced by radioactive impurities of 208Tl and 214Bi in the source of the double beta experiment NEMO-3 has been investigated. New methods of data analysis which decrease the background from the above-mentioned contamination are identified. The techniques can also be applied to other double beta decay experiments capable of measuring independently the energies of the two electrons.

The γ-ray flux in the Fréjus underground laboratory has been studied using an NaI detector surrounded by different diagonostic shields. Below 4MeV, the spectrum is dominated by radioactivities in the surrounding materials and rocks. Between 4 and 6MeV, the shape of the spectrum is well explained by U, Th and daughters, which are internal contaminations in the NaI crystal. Between 6 and 10MeV, the γ-ray flux is strongly correlated with neutron captures in the surrounding materials. Finally, the γ-ray flux above 10MeV falls off and is related to the very weak cosmic muon flux via muon bremsstrahlung.

To be sensitive to an effective Majorana neutrino mass, 〈mν〉, on the order of 0.1 eV, the NEMO 3 double beta (ββ(0ν)) decay experiment requires precise knowledge and control of the backgrounds. The effect of neutrons and γ-rays from the Fréjus underground laboratory (LSM, Laboratoire Souterrain de Modane) has been studied during 10700 h of data collection. The data were taken with a NEMO 2 prototype detector using different shield configurations. Monte Carlo calculations with GEANT/MICAP code and a new library of γ-rays from neutron captures are presented. The implied consequences for the NEMO 3 detector which is under construction are discussed. The neutrinoless double beta decay background induced by neutrons and γ-rays within the LSM will be suppressed to the very suitable level of 0.1 event in a live time of five years given the appropriate shield and magnetic field.