Measurement of the double-βdecay half-life ofNd150and search for neutrinoless decay modes with the NEMO-3 detector

Abstract

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...

Many-body correlations of quasiparticle random-phase approximation in nuclear matrix elements of neutrinolessdouble−βdecay

“…The latter value agrees well with the experimental value of 0.0579 ± 0.0032; this value is obtained from the average of three experimental half-lives [64] (for the experiments, see Refs. [65][66][67]) and the phase-space factor in Ref. [16].…”

Measurement of the two neutrino double beta decay half-life of Zr-96 with the NEMO-3 detector

“…The total mass of the enriched ZrO 2 is 22.0 g of which 9.4 ± 0.2 g is 96 Zr [7]. NEMO-3 results thus far are published in [8,9,10,11].…”

“…The difference never exceeds 5% for the internal backgrounds, therefore the uncertainty on the 2νββ half-life is estimated by fluctuating the internal backgrounds ± 5% and recording the corresponding change in 2νββ half-life. The world's best 2νββ half-life measurements for 150 Nd [21,11] and 48 Ca [22] have been recently obtained. These isotopes neighbor the 96 Zr source and are included as backgrounds.…”

Large ν ‐ ν ¯ $$ \nu \hbox{-} \overline{\nu} $$ oscillations from high-dimensional lepton number violating operator

“…As a result, it is concluded that the new long-range mode induced by O 7 gives the dominant contribution to the 0νββ decays in the present scenario. By comparing the current experimental limits on the 0νββ half-life of different nuclei [64][65][66][67][68][69][70], we can actually give the strong constraints to the Wilson coefficient C ud ee by assuming Λ ∼ 1 TeV. The numerical limits are collected in table 1, from which it is seen that the strongest constraint is given by the target 136 Xe [65,66] with |C ud ee | < 1.9 × 10 −4 .…”