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Double Beta Decay

(Observed for several nuclei, test of nuclear matrix elem. calculations). 0 : (A,Z)  (A,Z+2) + 2e -. u. e -. d. 2 : (A,Z)  (A,Z+2) + 2e - + 2 n e. n e. W -. L=2. n e. W -. d. e -. u. 1/t = G(Q,Z) |M nucl | 2 m ee 2 ,. m ee = |  i U ei ² m i |.

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Double Beta Decay

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  1. (Observed for several nuclei, test of nuclear matrix elem. calculations) 0: (A,Z)  (A,Z+2) + 2e- u e- d 2:(A,Z)  (A,Z+2) + 2e- + 2ne ne W- L=2 ne W- d e- u 1/t = G(Q,Z) |Mnucl|2 mee2, mee= |iUei ²mi | Double Beta Decay

  2. F.Feruglio, A. Strumia, F. Vissani, NPB 637 Degenerate | mee| in eV Goal of next generation experiments: ~10 meV Inverted hierarchy 90% CL Negligible errors from oscillations; width due to CP phases Normal hierarchy Lower bounds! Lightest neutrino (m1) in eV mee = f(m1, m²sol, m²atm, 12 , 13, -) from oscillation experiments Range of meederivedfrom solar and atmospheric oscillation experiments

  3. Experimental status of running experiments Heidelberg – Moscow:MPIK Heidelberg, Kurchatov Institute Location:Gran Sasso Underground Laboratory Source = detector, 76Ge (10.9 kg isotopically enriched ( 86%)): Q = 2038 keV CUORICINO (Cryogenic Underground Observatory for Rare Events): Firenze, Gran Sasso, Insubria, LBNL, Leiden, Milano, Neuchatel, South Carolina, Zaragoza Location:Gran Sasso Underground Laboratory Source = detector, TeO2 (40 kg)  130Te (13 kg): Q = 2615 keV NEMO3 (Neutrino Ettore Majorana Observatory): CENBG Bordeaux, Charles Univ. Prague, FNSPE Prague, INEEL, IReS Strasbourg, ITEP Moscow, JINR Dubna, Jyvaskyla Univ., LAL Orsay, LPC Caen, LSCE Gif, Mount Holyoke College, Saga Univ, UCL London Location: Frejus Underground Laboratory Source  detector study of different nuclei; main target 100Mo (6.9 kg): Q = 3034 keV NB: More than one nuclei needed to check systematics from nuclear matrix elements

  4. NEMO3 • Source in form of foils: 1SOURCE 2TRACKING VOLUME 3CALORIMETER • Tracking volume with Geiger cells • e+/e- separationby magnetic field • Plastic scintillators for calorimetry and timing Start data taking February 2003

  5. NEMO3: first results First results on 100Mo (650 h) V. Vasiliev (Nemo coll.) 2n spectrum t1/22n(y) = 7.8 ± 0.09 stat± 0.8 syst 1018 y t1/20n(y) > 6  1022 y Expected final sensitivity: 0.2 – 0.4 eV (6.9 kg) mee < 1.8 – 2.9 eV (C. Augier, ECT Trento)

  6. 2615 keV 208Tl single escape 208Tl double escape 208Tl CUORICINO Start data taking february 2003 Energy resolution: 7 keV FWHM TeO2 (40 kg)  130Te (13 kg): Q = 2615 keV Calibration spectrum 0.8 m (A. Giuliani, Taup03)

  7. anticoincidence background spectrum, only 5x5x5 crystals Background level 0.23 .04 c/keV/kg/y CUORICINO: first results t1/20n> 5  1023 y mee < 0.58 – 1.4 eV (90% c.l.) 3 y sensitivity (with present performance): 1  1025 y  mee < 0.13 – 0.31 eV (A. Giuliani, Taup03)

  8. New concept under study: Ge in liquid Ar – new ideas • Replace LN (LN=0.8 g/cm³, 77 K) by LAr (LN=1.4 g/cm³, 87 K)  LAr/ LN (2.615 MeV) = 0.62 • Scintillation yield: 40,000 photons / MeV  Active shielding medium! (4 x organic liquid scintillator) Emission in XUV (~130 nm) • Wavelength shifting required : Organic WLS or Xe addition • Essential for cosmogenic activities: Co-60, Ge-68, … • What’s about Ar-39, Ar-42 ?

  9. 76Ge: sensitivity, exposure and background 0.0001 0.001 0.01 0.06 / (kg year keV) HEIDELBERG-MOSCOW Collaboration, Eur. Phys. J. A 12 (2001) 147: M·T = 35.5 kg y, b = 6 ·10-2 (kg y keV), DE ~ 4.2 keV Sensitivity (with bgd): mee (b DE / M T)1/4

  10. Basic concepts about 76Ge in liquid N2 • background sources external to crystals • clean contacts and support can be realized • minimization of surface contaminations • purification of liquid nitrogen Operation of ‘naked’ Ge-detecctors In liquid nitrogen: G. Heusser, Ann. Rev. Nucl. Part. Sci. (1995) GENIUS proposal: H.V. Klapdor-Kleingrothaus, J. Hellmig, M. Hirsch (1997); H.V. Klapdor–Kleingrothaus, L. Baudis, G. Heusser, B. Majorovits, H. Paes (1999), hep-ph/9910205

  11. LN2 shield against external background radiation LNGS: ~ 107 /m²/d (2.6 MeV ) ~6 m 10-4 (kg keV y) -1 LN2

  12. Space @ LNGS ~14 m 14.80 m

  13. LN/LAr facility: Design study (b)

  14. How small could a tank be? • Lead layer submersed in LAr • 232Th activity of lead  tank Ø • Preliminary results 30Bq/kg 

  15. Active suppression of internal bgd: example 60Co • Cosmogenic activities: • Production after completion of crystal growth • Exposure to cosmic rays above ground for 10 days: 0.18 Bq/kg [GENIUS]

  16. , Wavelength shifter Reflector (VM2000) Reduction factor ~100 60Co: no vs. active suppression

  17. Bgd. in LAr: example 42Ar 42Ar / natAr = 3·10-21 (30 Bq/kg) [Barabash et al., LAr-TPC @ LNGS]

  18. Wavelength shifter Reflector (VM2000) 42Ar: no vs. active suppression , 1,2 No issue for DBD even without active suppression!

  19. External bgd: example 2.615 MeV gamma 232Th (208Tl) in lead shield Flux from rocks(0.5 Bq / kg) and concrete (5 Bq / kg) @ LNGS: 3.5 ·107 / (m² d) [BOREXINO, Laubenstein] New lead for shielding under study with GEMPI @ LNGS: <30 Bq / kg

  20. Wavelength shifter Reflector (VM2000) 232Th (208Tl): no vs. active suppr.  Lead Simulation for 30 Bq/kg, inner-Ø: 2m, height: 2 m

  21. Summary and outlook (1) • DBD unique tool to study neutrino properties: Majorana vs. Dirac, mass scale, hierarchy, CP phases • Oscillation data make distinct predictions for mee (NH: 1-4 meV, IV: 14-57 eV, DG: <1 eV (90% CL)) • Second generation experiments (NEMO3, CUORICINO) started data taking; sensitive to check HdM claim within next years: ~ 0.1-0.4 eV

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