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Advances in Double Beta Decay Experiments: Techniques and Results

This study explores the experimental progress in double beta decay (0νββ and 2νββ) using various nuclei. Key technologies in underground laboratories (e.g., Gran Sasso) are highlighted, including isotope-enriched detectors like 76Ge and 130Te. Notable experiments such as CUORICINO and NEMO3 are discussed, showcasing their sensitivities and methodologies in measuring effective neutrino masses (mee). The challenges posed by background noise and new experimental concepts, including the use of liquid Argon for the detection of cosmogenic activities, are also addressed.

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Advances in Double Beta Decay Experiments: Techniques and Results

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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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