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The NEMO Experiment

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The NEMO (Neutrino Ettore Majorana Experiment) international collaboration was established to look for the 2β(0ν) decay mode, and this started way back in 1988. The NEMO3 detector contained around 10 kg of a double-beta emitting source. Each of its 20 independent sectors contained a source foil surrounded by both a wire chamber and a calorimeter.

Because of this hybrid tracking calorimeter, NEMO3 was a world-wide unique experiment, namely the only one to be able to distinguish between the various detected particles.

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Détecteur Nemo3 dans le laboratoire souterrain de Modane

Data acquisition began in february 2003 and the experiment lead to very interesting results. To start with, data from phase I (ending in december 2004) gave way to a precise value of the 2β(2ν) half-life of 100Mo:

T_{1/2}(ββ(2ν); Mo) = 7,11 \pm 0,02~(stat) \pm 0,54~(stat)\times 10^{18} \text{ans,}

and of 82Se:

T_{1/2}(ββ(2ν); Se) = 9,6 \pm 0,3~(stat) \pm 0,54~(syst) \times 10^{19} \text{ans.}

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Données obtenues pour le 100Mo, avec à droite un agrandissement de la partie du spectre où est attendu le signal ββ(0ν)

For Mo, the absence of a ββ(0ν) signal gave a limit on the period T1/2(ββ(0ν)) > 4.6 \times 10^{23} years. Likewise, for Se, the value was set to > 1.0 \times 10^{23} years. A limit on the effective neutrino mass, in regard of these measurments, was m_\nu < 0.7-2.8 eV. Therefore the SuperNemo project aiming at lowering the sensitivity down to 50 meV.

NEMO official site

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Vue de l’intérieur de la chambre à fils de NEMO3 pendant le démontage : surfaces réflectrices des murs du calorimètre et supports en cuivre des fils des cellules Geiger.