A. Smolnikov

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 Frejus underground laboratory since February 2003, is devoted to the search for neutrinoless double beta decay (bb0nu). Half-lives of the two neutrino double beta decays (bb2nu) 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 ~7kg of 100Mo and ~1 kg of 82Se. The corresponding lower limits for the half-lives are 4.6 x 10^23 years for 100Mo and 1.0 x10^23 years for 82Se (90% C.L.). Depending on the nuclear matrix elements calculation, limits for the effective Majorana neutrino mass are<0.7-2.8 eV for 100Mo and<1.7-4.9 eV for 82Se

Technical design and performance of the NEMO 3 detector

Abstract The development of the Neutrino Ettore Majorana Observatory (NEMO ∼ 3 ) 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 NEMO 3 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.

Measurement of the Double Beta Decay Half-life of Nd-150 and Search for Neutrinoless Decay Modes with the NEMO-3 Detector

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.

Limits on different Majoron decay modes of Mo-100 and Se-82 for neutrinoless double beta decays in the NEMO-3 experiment

Abstract The NEMO-3 tracking detector is located in the Frejus 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 ( T 1 / 2 > 2.7 × 10 22 yr ) and 82Se ( T 1 / 2 > 1.5 × 10 22 yr ) have been obtained. Corresponding bounds on the majoron–neutrino coupling constant are 〈 g e e 〉 ( 0.4 – 1.8 ) × 10 −4 and ( 0.66 – 1.9 ) × 10 −4 .

Measurement of double beta decay of Mo-100 to excited states in the NEMO 3 experiment

The double beta decay of 100Mo to the 0^+_1 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 0^+_1 state is measured to be T^(2nu)_1/2 = [5.7^{+1.3}_{-0.9}(stat)+/-0.8(syst)]x 10^20 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 0^+_1 state has been found. The corresponding half-life limit is T^(0nu)_1/2(0^+ -->0^+_1)>8.9 x 10^22 y (at 90% C.L.). The search for the double beta decay to the 2^+_1 excited state has allowed the determination of limits on the half-life for the two neutrino mode T^(2nu)_1/2(0^+ -->2^+_1)>1.1 x 10^21 y (at 90% C.L.) and for the neutrinoless mode T^(0nu)_1/2(0^+ -->2^+_1)>1.6 x 10^23 y (at 90% C.L.).

Search for neutrinoless double-beta decay of

We report the results of a search for the neutrinoless double-β decay (0νββ) of Mo100, using the NEMO-3 detector to reconstruct the full topology of the final state events. With an exposure of 34.7  kg·y, no evidence for the 0νββ signal has been found, yielding a limit for the light Majorana neutrino mass mechanism of T1/2(0νββ)>1.1×1024 years (90% C.L.) once both statistical and systematic uncertainties are taken into account. Depending on the nuclear matrix elements this corresponds to an upper limit on the Majorana effective neutrino mass of ⟨mν⟩<0.3–0.9  eV (90% C.L.). Constraints on other lepton number violating mechanisms of 0νββ decays are also given. Searching for high-energy double electron events in all suitable sources of the detector, no event in the energy region [3.2–10] MeV is observed for an exposure of 47  kg·y.

^{100}Mo

Double beta decay of 100Mo to the excited states of daughter nuclei has been studied using a 600 cm3 low-background HPGe detector and an external source consisting of 2588 g of 97.5% enriched metallic 100Mo, which was formerly inside the NEMO-3 detector and used for the NEMO-3 measurements of 100Mo. The half-life for the two-neutrino double beta decay of 100Mo to the excited View the MathML source01+ state in 100Ru is measured to be T1/2=[7.5±0.6(stat)±0.6(syst)]⋅1020 yrT1/2=[7.5±0.6(stat)±0.6(syst)]⋅1020 yr. For other (0ν+2ν)(0ν+2ν) transitions to the View the MathML source21+, View the MathML source22+, View the MathML source02+, View the MathML source23+ and View the MathML source03+ levels in 100Ru, limits are obtained at the level of ∼(0.25-1.1)⋅1022 yr∼(0.25-1.1)⋅1022 yr.

with the NEMO-3 detector

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.

Investigation of double beta decay of 100Mo to excited states of 100Ru

The NEMO-3 experiment at the Modane Underground Laboratory has investigated the double-

Measurement of the Double Beta Decay Half-life of 130Te with the NEMO-3 Detector

\beta