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Double beta decay and Majorana neutrinos

Double beta decay and Majorana neutrinos. Ettore Fiorini, Venice March 8, 2007. → → <= =>. Majorana =>1937. Presently an essential problem in neutrino and in astroparticle physiss.

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Double beta decay and Majorana neutrinos

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  1. Double beta decay and Majorana neutrinos Ettore Fiorini, Venice March 8, 2007 → → <= => Majorana =>1937 Presently an essential problem in neutrino and in astroparticle physiss

  2. The most sensitive way to investigate the Dirac or Majorana nature of the neutrino is neutrinoless double beta decay (DBD)This very rare process was sugested in general form by Maria Goepper Mayer just one year after the Fermi theory of beta decay. Also Bruno Pontecorvo was deeply involved.

  3. Double Beta –DisintegrationM.Goeppert-Mayer, The John Hopkins University(Received May, 20 , 1935)From the Fermi theory of b- disintegration the probability of simultameous emission of two electrons (and two neutrinos) has been calculated. The result is that this process occurs sufficiently rarely to allow an half-life of over 1017 years for a nucleus, even if its isobar of atomic number different by 2 were more stable by 20 times the electron mass Double beta decay was at the beginning searched In the neutrinoless channel as a powerful way to search for lepton number non conservation. Presently it is also considered as the most powerful way to investigate the value of the mass of a Majorana neutrino

  4. 1. (A,Z) => (A,Z+2) + 2 e- + 2 ne¯2. (A,Z) => (A,Z+2) + 2 e- + c ( …2,3 c)3. (A,Z) => (A,Z+2) + 2 e- Process 1 has been detected in ten nuclei Process2 and 3. violate the lepton number Process 3, normally called neutrinoless DBD, would be revealed by the presence of a peak in the sum of the electron energies => <mn>≠ 0

  5. - - e - e u e d n W e u W n e d W d u d W - e u 2n - bb decay n n e e 0n - bb decay Neutrinoless bb decay

  6. Phase space Nuclear matrix elements EffectiveMajorana neutrino mass rateof DDB-0n 1/t= G(Q,Z) |Mnucl|2 <mn>2 The rate of neutrinoless DBD strongly depends on the evaluation of the nuclear matrix elements, quite uncertain so far Need to search for neutrinoless DBD in various nucleiA pick could be due to some unforeseen background peak

  7. Possible schemes for neutrino masses

  8. New calculations by.S.Pascoli and S.T.Petkov

  9. detector e- e- source e- e- detector SourceDetector Experimental approaches Geochemical experimentsi82Se = > 82Kr, 96Zr = > 96Mo (?) , 128Te = > 128Xe (non confirmed), 130Te = > 130TeRadiochemical experiments238U = > 238Pu (non confirmed) Direct experiments Source = detector (calorimetric) Sourcedetector

  10. heat bath Thermal sensor absorber crystal Incident particle Cryogenic detectors

  11. DE @ 5 keV ~100 mk ~ 1 mg<1 eV ~ 3 eV @ 2 MeV ~10 mk ~ 1 kg<10 eV ~ keV

  12. 210Po a line Counts Energy [keV] Resolution of the 5x5x5 cm3 (~ 760 g ) crystals : 0.8 keV FWHM @ 46 keV 1.4 keV FWHM @ 0.351 MeV 2.1 keV FWHM @ 0.911 MeV 2.6 keV FWHM @ 2.615 MeV 3.2 keV FWHM @ 5.407 MeV (the best a spectrometer ever realized)

  13. Present experimental situation

  14. In December 2001, 4 authors (KDHK) of the HM collaboration announce the discovery of neutrinoless DBD t1/20n(y) = (0.8 – 18.3)  1025 y (1  1025 y b.v.) Mbb= 0.05 - 0.84 eV (95% c.l.) 2004 2001 54.98 kg•y 2.2 s 71.7 kg•y 4 s better results in 2004 skepticism in DBD community in 2001 HM collaboration subset (KDHK): claim of evidence of 0n-DBD

  15. Two new experimentsNEMO III and CUORICINO

  16. bb2n measurement bb0n search 116Cd405 g Qbb = 2805 keV 96Zr 9.4 g Qbb = 3350 keV 150Nd 37.0 g Qbb = 3367 keV 48Ca 7.0 g Qbb = 4272 keV 130Te454 g Qbb = 2529 keV External bkg measurement natTe491 g 100Mo6.914 kg Qbb = 3034 keV 82Se0.932 kg Qbb = 2995 keV Cu621 g

  17. 0n analysis 100Mot1/20n(y) > 4.6  1023 Mbb< 0.7 – 2.8 eV (90% c.l.) 82Set1/20n(y) > 1.0  1023 Mbb< 1.7 – 4.9 eV (90% c.l.)

  18. CUORICINO

  19. Search for the 2b|on in 130Te (Q=2529 keV) and other rare events • At Hall A in the Laboratori Nazionali del Gran Sasso (LNGS) • 18 crystals 3x3x6 cm3 + 44 crystals 5x5x5 cm3 = 40.7 kg of TeO2 • Operation started in the beginning of 2003 => ~ 4 months • Background .18±.01 c /kev/ kg/ a 2modules, 9detector each, crystal dimension3x3x6 cm3 crystal mass330 g 9 x 2 x 0.33 = 5.94 kg of TeO2 11modules, 4detector each, crystal dimension5x5x5 cm3 crystal mass790 g 4 x 11 x 0.79 = 34.76 kg of TeO2

  20. detail MT = 5.87 (kg 130Te) x y anticoincidence spectrum 208Tl line b = 0.18  0.02 c/keV/kg/y (Jul 2005) DBD 60Co pile-up peak 130Te DBD Q-value Energy [keV] Present CUORICINO result (new) t >3 x 1024 (90 % c.l.) 8.35 kg year of 130Te <m0n> < .16 - .9 eV => Klapdor et al m0n < .1- .9 eV

  21. DBD and Neutrino Masses Present Cuoricino region Arnaboldi et al., submitted to PRL, hep-ex/0501034(2005). Possible evidence (best value 0.39 eV) H.V. Klapdor-Kleingrothaus et al., Nucl.Instrum.and Meth. ,522, 367 (2004). With the same matrix elements the Cuoricino limit is 0.53 eV “quasi” degeneracy m1 m2  m3 Inverse hierarchy m212= m2atm Direct hierarchy m212= m2sol Cosmological disfavoured region (WMAP) Feruglio F. , Strumia A. , Vissani F. hep-ph/0201291

  22. Next generation experiments

  23. Ionization

  24. Ionization COBRA

  25. C0BRA Use large amount of CdZnTe Semiconductor Detectors Array of 1cm3 CdTe detectors K. Zuber, Phys. Lett. B 519,1 (2001)

  26. Nd dissolved in SNO => tons of material; Scintillation • 0n: 1000 events per • year with 1% natural • Nd-loaded liquid • scintillator in SNO++ by Alex Wright simulation: one year of data maximum likelihood statistical test of the shape to extract 0n and 2n components…~240 units of Dc2 significance after only 1 year!

  27. Scintillation

  28. Tracking SUPERNEMO

  29. Tracking

  30. 2P1/2 650 nm 493 nm 4D3/2 metastable 47s 2S1/2 EXO • concept: scale Gotthard experiment adding Ba tagging to suppress background (136Xe136Ba+2e) • single Ba detected by optical spectroscopy • two options with 63% enriched Xe • High pressure Xe TPC • LXe TPC + scintillation • calorimetry + tracking • expected bkg only by -2 • energy resolution E = 2% Present R&D • Ba+ spectroscopy in HP Xe / Ba+ extr. • energy resolution in LXe (ion.+scint.) • Prototype scale: • 200 kg enriched L136Xe without tagging • all EXO functionality except Ba id • operate in WIPP for ~two years • Protorype goals: • Test all technical aspects of EXO (except Ba id) • Measure 2n mode • Set decent limit for 0n mode (probe Heidelberg- Moscow) LXe TPC Full scale experiment at WIPP or SNOLAB • 10 t (for LXe ⇒ 3 m3) • b = 4×10-3 c/keV/ton/y • 1/21.3×1028 y in 5 years • 〈m〉 0.013 ÷ 0.037 eV

  31. disfavoured by cosmology CUORE expected sensitivity In 5 years: Strumia A. and Vissani F. hep-ph/0503246

  32. Other possible candidates for neutrinoless DBD 130Te has high transition energy and 34% isotopic abundance => enrichment non needed and/or very cheap. Any future extensions are possible Performance of CUORE, amply tested with CUORICINO

  33. How deep should we go?

  34. Total Muon Flux v.s. Depth Relative to Flat Overburden (cm-2 s-1) Total Depth (km.w.e) Relative to Flat Overburden

  35. Neutron Flux at Underground Sites

  36. eg. Study for 60 kg Majorana Module

  37. CONCLUSIONS Neutrino oscillationsDm2 ≠0 <mn> finite for at leaqst one neutrino Neutrinoless double beta decay would indicateif neutrino is alepton violatingMajorana particle and would allow in this case to determine <mn> and the hierachy of oscillations. This process has been indicated by an experiment (Klapdor) with a value of ~0.44 eV but has not yet confirmed Future experiments on neutrinoless double beta decay will allow to reach the sensitivity predicted by oscillations The multidisciplinarity of searches on double beta decay involves nuclear and e subnuclear physics, astrophysics , radioactivity, material science, geochronology etc. It could help in explaining the particle-antiparticle asymmetry of the Universe

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