Ts. Vylov

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.

Double-β decay of 82Se

Abstract The NEMO-2 tracking detector located in the Frejus Underground Laboratory was designed as a prototype of the NEMO-3 detector to study neutrinoless (Oν) and two neutrino (2ν) double-beta decay (ββ) physics. After 10357 h of running with an isotopically enriched selenium source (2.17 mol yr of 82Se) a ββ2ν decay half-life of T 1 2 = (0.83 ± 0.10( stat ) ± 0.07 ( syst )) × 10 20 yr was measured. Limits with a 90% C.L. on the 82Se half-lives of 9.5 × 1021 yr for ββ0ν decay to the ground state, 2.8 × 1021 yr to the (2+) excited state and 2.4 × 1021 yr for ββ0νχ0 decay with a Majoron (χ0) were also obtained.

Double beta decay of 96Zr

Abstract After 10357 h of running the NEMO-2 tracking detector with an isotopically enriched zirconium source (0.084 mol yr of 96Zr), a ββ2ν decay half-life of T1/2=(2.1+0.8(stat)−0.4(stat)±0.2(syst))·1019 y was measured. Limits with a 90% C.L. on the 96Zr half-lives of 1.0·1021 y for ββ0ν decay to the ground state, 3.9·1020 y to the 2+ excited state and 3.5·1020 y for ββ0νχ0 decay with a Majoron (χ0) were obtained. The data also provide direct limits at the 90% C.L. for the 94Zr half-lives. These limits are 1.1·1017 y for ββ2ν decay to the ground state, 1.9·1019 y for ββ0ν decay to the ground state and 2.3·1018 y for ββ0νχ0 decay to ground state.

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 .

A new combined electrostatic electron spectrometer

Abstract A new electrostatic electron spectrometer is described which incorporates an electron retarding device in series with a double cylindrical mirror-analyser. The spectrometer was particularly designed for measuring low energy electrons and has an upper energy limit ∼ 50 keV. The resolution can be changed easily according to need, and the energy may be determined, relatively to standards, with a precision amounting to 1 eV in the best conditions.

Performance of a prototype tracking detector for double beta decay measurements

Abstract To investigate double beta decay processes, the NEMO collaboration began a long-range research and development program in 1988. The NEMO 2 detector, which is now running in the Frejus underground laboratory (L.S.M. Laboratoire Souterrain de Modane), is the second prototype. It consists of a 1 m2 source foil sandwiched between Geiger cell drift chambers for electron tracking and two plastic scintillator walls for energy and time-of-flight measurements. The technical description of the detector is followed by the study of the various sources of background.

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 double beta decay of 48Ca in the TGV experiment

Abstract This Letter describes a collaborative TGV (Telescope Germanium Vertical) study of the double beta decay of 48 Ca with a low-background and high sensitivity Ge multi-detector spectrometer. The results of T 1/2 2 νββ =(4.2 +3.3 −1.3 )×10 19 years and T 1/2 0 νββ >1.5×10 21 years (90% CL) for double beta decay of 48 Ca were found after processing experimental data obtained after 8700 hours of measuring time, using approximately 1 gramme of 48 Ca. The features of a TGV-2 experiment are also presented.