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.

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

The half-life for double beta decay of 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 150 Nd the half-life for 2νββ decay is measured to be T 2ν 1/2 = (9.11 +0.25 −0.22 (stat.) ± 0.63 (syst.)) × 10 18 years. The observed limit on the half-life for neutrinoless double beta decay is found to be T 0ν 1/2 > 1.8×10 22 years at 90% Confidence Level. This translates into a limit on the effective Majorana neutrino mass of mν < 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. Experiments studying atmospheric, solar, reactor and accelerator neutrinos have established the existence of neutrino oscillations as a direct evidence for a non-zero neutrino mass. These experiments, however, cannot distinguish between Dirac or Majorana neutrinos. They also provide no information on the absolute neutrino mass scale, since oscillations experiments measure the square of the mass difference between neutrino states. The half-life of neutrinoless double beta decay (0νββ) is inversely proportional to the effective Majorana neutrino mass squared, m ν 2 . Observation of this process would therefore directly constrain the neutrino mass scale and would be unambiguous evidence for the Majorana nature of neutrinos. The 0νββ process also violates lepton number and is therefore a direct probe for physics beyond the standard model of particle physics.The search for neutrinoless double beta decay of neodymium-150 ( 150 Nd) using the NEMO-3 detector is of special interest since 150 Nd is a candidate isotope for SuperNEMO [1], a next generation double beta decay experiment based on the NEMO-3 concept, and the SNO++ experiment at SNOLAB [2]. Its main advan-2 tages are the high Q ββ value for double beta decay, Q ββ = 3.368 MeV, which lies above the typical energies for many background sources, and the large phase space factor. The 2νββ half-life of 150 Nd has previously been measured using a Time Projection Chamber [3,4].The NEMO-3 experiment has been taking data since 2003 in the Modane Underground Laboratory (LSM) located in the Fréjus tunnel at a depth of 4800 m water equivalent. The detector has a cylindrical shape with 20 sectors that contain different isotopes in the form of thin foils with a total surface of about 20 m 2 [5]. In addition to ∼7 kg of 100 Mo and ∼1 kg of 82 Se, the detector contains smaller amounts of other isotopes. The neodymium source foil is composed of Nd 2 O 3 with an enrichement of (91 ± 0.5)%, corresponding to a 150 Nd mass of 36.55 ± 0.10 g. On each side of the foils is a ∼50 cm wide tracking volume comprising a total of 6180 drift cells operated in Geiger mode with helium as drift gas. A 25 Gauss magnetic field created by a solenoid provides charge identification. The calorimeter consists of 1940 plastic scintillators coupled to low radioactivity photomultipliers. For 1 MeV electrons the energy resolutio...

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 100 Mo and 82 Se 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 100 Mo (T 1/2 > 2.7 · 10 22 y) and 82 Se (T 1/2 > 1.5 · 10 22 y) have been obtained. Corresponding bounds on the Majoronneutrino coupling constant are g ee < (0.4 − 1.9) · 10 −4 and < (0.66 − 1.7) · 10 −4 .

23 pages, 7 figures, 4 tables, submitted to Nucl. PhysThe 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.{+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.)