Neutrino Ettore Majorana Observatory

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The Neutrino Ettore Majorana Observatory (NEMO experiment) is an international collaboration of scientists searching for neutrinoless double beta decay (0νββ). Observation of 0νββ would indicate neutrinos are Majorana particles and could be used to measure the neutrino mass. It is located in the Modane Underground Laboratory (LSM) in the Fréjus Road Tunnel. Data taking started in January 2003 and ended in January 2011. The NEMO-2 and NEMO-3 detectors produced measurements for double neutrino decays and limits for neutrinoless double-beta decay for a number of elements, such as molybdenum-100 and selenium-82. These double beta decay times are important contributions to understanding the nucleus and are needed inputs for neutrinoless decay studies, which constrain neutrino mass.

The NEMO collaboration remains active[1] and is constructing an improved SuperNEMO detector.

Experiment[edit]

Other 0νββ experiments use the same material for the source of double beta decays and the detector. This allows a large mass of source material to be used and thereby maximizes the sensitivity of the experiment, but limits its flexibility. NEMO takes a different approach, using thin foils of source material surrounded by a separate tracking calorimeter.

This allows the use of any source material which can be formed into a thin foil. Also, because its tracking is more accurate, it can reliably detect if two electrons come from the same place, thereby reducing false detections of double beta decays.

The experiment has a cylindrical shape with 20 sectors that contain different isotopes in the form of thin foils with a total surface of about 20 m2. The main isotopes used for the neutrinoless double beta decay search are about 7 kg of enriched molybdenum-100 and about 1 kg of selenium-82. The experiment also contains smaller amounts of cadmium-116, neodymium-150, zirconium-96 and calcium-48 foils. Tellurium and copper foils are used for background measurements.

A tracking detector on each side of the foil detects electrons and positrons from the double beta decay. They are identified by their curvature in a magnetic field and particle energy is measured in a calorimeter. In 0νββ, the sum of the electron and positron energies will be the(Q value) released in double beta decay. For standard double beta decay the neutrinos, which cannot be observed directly, reduce the detected energy.

Results[edit]

Neutrinoless double beta decay (0νββ) has not been observed in 5 years of data taking and limits have been set for several isotopes.

NEMO-2 reported 0νββ limits for Majoron models of 100Mo, 116Cd, 82Se and 96Zr.[2]

NEMO-3 reported precision 2νββ half-lives for its 7 isotopes and 0νββ limits for 96Zr, 48Ca, 150Nd at Neutrino08.[3]

NEMO-3 reported 2νββ and more 0νββ limits at SUSY08.[4]

In 2014, NEMO-3 reported a 47 kg⋅y search for 0νββ of molybdenum-100 yielded T1/2 > 1.1×1024 years. This can be translated into an upper limit on the effective neutrino mass: mv < 0.3–0.9 eV, depending on the nuclear model.[5]

NEMO 2νββ Half-life Measurements

Nuclide Half-life, years
48Ca 4.4+0.5
−0.4
± 0.4 ×1019
82Se 9.6 ± 0.3 ± 1.0 ×1019
96Zr 2.35 ± 0.14 ± 0.16 ×1019
116Cd 2.8 ± 0.1 ± 0.3 ×1019
130Te 7.0 ± 0.9(stat) ± 1.1(syst) ×1020[6]
150Nd 9.11+0.25
−0.22
± 0.63 ×1018
100Mo 7.11 ± 0.02(stat) ± 0.54(syst) ×1018

NEMO Highest 0νββ Decay Lower Limits

Isotope T1/2 (yr) Neutrino mass limit (eV)
82Se 2.1×1023
100Mo 1.1×1024 0.9
116Cd 1.6×1022
96Zr 8.6×1021 20.1
150Nd 1.8×1022 6.3
48Ca 1.3×1022 29.7

The 96Zr decay is particularly relevant because of its high Q and use in searches for time-dependence of the physical constants. Geochemical measurements of ZrSiO4 allow comparison of its historic and present rates,[7] by extracting the resultant 96Mo.

SuperNEMO[edit]

A next generation experiment, SuperNEMO, is under construction. It is based on technology used by the NEMO-3 experiment, but will be more than a factor of ten bigger.[8] The SuperNEMO detector will consist of 20 modules each containing approximately 5 kg of enriched double beta decay emitting isotope in the form of a thin foil. The installation of a first module (using selenium-82) in the LSM is under way, with data taking expected in the second half of 2015.[9]

References[edit]

  1. ^ "NEMO3 / SuperNEMO International Collaboration Meeting". Caen. 13–16 October 2014. Retrieved 2015-04-23. 
  2. ^ NEMO collaboration (9 October 2000). "Limits on different Majoron decay modes of 100Mo, 116Cd, 82Se and 96Zr for neutrinoless double beta decays in the NEMO-2 experiment" (PDF). Nuclear Physics A. 678 (3): 341–352. Bibcode:2000NuPhA.678..341A. doi:10.1016/S0375-9474(00)00326-2. 
  3. ^ Flack, R. L.; for the NEMO 3 collaboration (2008). "Results from NEMO 3". Journal of Physics: Conference Series. 136 (2): 022032. arXiv:0810.5497Freely accessible. doi:10.1088/1742-6596/136/2/022032. 
  4. ^ NEMO 3 Collaboration (2008). "Neutrinoless double beta decay search with the NEMO 3 experiment". AIP Conf. Proc. 1078 (1078): 332–334. Bibcode:2008AIPC.1078..332N. arXiv:0810.0637Freely accessible. doi:10.1063/1.3051951. 
  5. ^ NEMO-3 Collaboration (2014). "Search for Neutrinoless Double-Beta Decay of 100Mo with the NEMO-3 Detector". Phys. Rev. D. 89 (11): 111101. Bibcode:2014PhRvD..89k1101A. arXiv:1311.5695Freely accessible. doi:10.1103/PhysRevD.89.111101. 
  6. ^ Arnold, R.; Augier, C.; Baker, J.; Barabash, A. S.; Basharina-Freshville, A.; Blondel, S.; Bongrand, M.; Broudin-Bay, G.; Brudanin, V.; Caffrey, A. J.; Chapon, A.; Chauveau, E.; Durand, D.; Egorov, V.; Flack, R.; Garrido, X.; Grozier, J.; Guillon, B.; Hubert, Ph.; Hugon, C.; Jackson, C. M.; Jullian, S.; Kauer, M.; Klimenko, A.; Kochetov, O.; Konovalov, S. I.; Kovalenko, V.; Lalanne, D.; Lamhamdi, T.; Lang, K.; Liptak, Z.; Lutter, G.; Mamedov, F.; Marquet, Ch.; Martin-Albo, J.; Mauger, F.; Mott, J.; Nachab, A.; Nemchenok, I.; Nguyen, C. H.; Nova, F.; Novella, P.; Ohsumi, H.; Pahlka, R. B.; Perrot, F.; Piquemal, F.; Reyss, J. L.; Richards, B.; Ricol, J. S.; Saakyan, R.; Sarazin, X.; Simard, L.; Šimkovic, F.; Shitov, Yu.; Smolnikov, A.; Söldner-Rembold, S.; Štekl, I.; Suhonen, J.; Sutton, C. S.; Szklarz, G.; Thomas, J.; Timkin, V.; Torre, S.; Tretyak, V. I.; Umatov, V.; Vála, L.; Vanyushin, I.; Vasiliev, V.; Vorobel, V.; Vylov, Ts.; Zukauskas, A.; et al. (NEMO-3 Collaboration) (4 August 2011). "Measurement of the ββ Decay Half-Life of 130Te with the NEMO-3 Detector". Physical Review Letters. 107 (6): 062504. PMID 21902318. arXiv:1104.3716Freely accessible. doi:10.1103/PhysRevLett.107.062504. 
  7. ^ Wieser, Michael; De Laeter, John (2001). "Evidence of the double β decay of zirconium-96 measured in 1.8×109 year-old zircons". Physical Review C. 64 (2): 024308. Bibcode:2001PhRvC..64b4308W. doi:10.1103/PhysRevC.64.024308. 
  8. ^ R. Arnold; et al. (2010). "Probing new physics models of neutrinoless double beta decay with SuperNEMO" (PDF). European Physical Journal C. 70 (4): 927–943. Bibcode:2010EPJC...70..927A. arXiv:1005.1241Freely accessible. doi:10.1140/epjc/s10052-010-1481-5. 
  9. ^ Gómez Maluenda, Héctor (3 Jul 2014). Latest results of NEMO-3 experiment and present status of SuperNEMO. ICHEP2014: The 37th International Conference on High Energy Physics. Valencia. Retrieved 2015-04-23. SuperNEMO is at present under construction after a R&D phase (started in 2007) which concluded that all the requirements are achievable. First phase is the construction of a first module that has been started in 2012 and will finish during 2015, when the data taking is expected to start. 

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