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0 - Double Beta Decay Search: Status and Perspectives

0 - Double Beta Decay Search: Status and Perspectives. Stefan Sch önert ,MPIK KET workshop neutrino physics DESY-Hamburg 7.10.2003. 0  search and impact on neutrino properties Status and plans of running experiments Plans and outlook of the new MPIK DBD initiative.

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0 - Double Beta Decay Search: Status and Perspectives

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  1. 0-Double Beta Decay Search: Status and Perspectives Stefan Schönert ,MPIK KET workshop neutrino physics DESY-Hamburg 7.10.2003 • 0 search and impact on neutrino properties • Status and plans of running experiments • Plans and outlook of the new MPIK DBD initiative

  2. (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 L=2 ne W- ne W- d e- u Double Beta Decay • Majorana (not Dirac ! ) • see-saw models, Majorana CP phases, leptogenesis

  3. DBD observables: final state electrons • additional signatures: • single electron energy distribution • angular distribution

  4. Phase space  Q5 Nuclear matrix elements Effective Majorana mass complementarity Decay rate and neutrino properties (decay generated by (V-A) cc-interaction via exchange of three Majorana neutrinos) 0n-DBD rate 1/t = G(Q,Z) |Mnucl|2 mee2 mee= |iUei ²mi | NB: Beta-endpoint (Katrin) me = (i|Uei²|mi²)1/2

  5. m3 m²atm m2 m²sol m1 m3 m3 m²sol m2 Mass m²atm m²atm m2 m²sol m1 m1 IH DG NH Input for meefrom -oscillations Solar/Reactor -:12, m²solAtmosph.-:m²atmReaktor-:13 For NH: m2 = (m1² + m²sol )1/2 m3 = (m1² + m²sol + m²atm )1/2 mee= |cos²13(m1cos²12 + m2 e2isin²12) + m3 e2isin²13| mee = f(m1, m²sol, m²atm, 12, 13, -)

  6. 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 Lightest neutrino (m1) in eV Range of meederivedfrom oscillation experiments NH: 1-4 meV IV: 14-57 meV DG: <1 eV (90% CL) hierarchy, absolute mass scale, Majorana CP phases ,

  7. 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

  8. 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

  9. 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)

  10. 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)

  11. 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)

  12. Cuoricino  Cuore CUORE = closely packed array of 1000 detectors 25 towers - 10 modules/tower - 4 detector/module M = 790 kg Each tower is a CUORICINO-like detector Expected final sensitivity: If b = 0.01 counts/(keV kg y) mee < 28 – 68 meV If b = 0.001 counts/(keV kg y) mee < 16 – 38 meV (A. Giuliani, Taup03)

  13. Heidelberg-Moscow • Q(76Ge) = 2.039 MeV • 5 detectors operating @ LNGS • 10.96 kg active mass (86% enriched) • 125.5 mol of 76Ge t1/20n> 1.9  1025 y mee < 0.35 eV (90% c.l.) H.V. Klapdor-Kleingrothaus, A. Dietz, L. Baudis, G. Heusser, I.V. Krivosheina, S. Kolb, B. Majorovits, H. Paes, H. Strecker, V. Alexeev, A. Balysh, A.Bakalyarov, S.T. Belyaev, V.I. Lebedev, and S. Zhukov Eur. Phys. J. A 12 (2001) 147

  14. Heidelberg-Moscow Sum spectrum of 76Ge detectors Nr. 1,2,3,5 over the period August 1990 to May 2000, 46.502 kg y H.V. KLAPDOR-KLEINGROTHAUS, A. DIETZ, H.L. HARNEY, I.V. KRIVOSHEINA Mod. Phys. Lett. A 16 (2001) 2409 Peak searching procedure: evidence at 2.2  – 3.1 CL t1/20n= (0.8 – 18.3)  1025y (95% CL) (1  1025 y best value) mee = 0.11 - 0.56 eV (0.39 best value) H.V. Klapdor-Kleingrothausa, A. Dietz I.V. Krivosheina, C. Doerr, C. Tomei NIM A 510 (2003) 281–289 mee = 0.05 - 0.84 eV (95% CL) (attributing larger uncertainties to nuclear matrix elements) Sum spectrum, measured with the detectors Nr. 2,3,5 operated with pulse shape analysis in the period November 1995 to May 2000 (28.053 kg y)

  15. runs with “under-threshold events” runs without “under-threshold events” 6 counts 0 2035 2045 Heidelberg-Moscow Kurchatov Group of HdM-Exp. A.M. Bakalyarov, A.Ya. Balysh, S.T. Belyaev, V.I. Lebedev, S.V. Zhukov NANP2003, Dubna hep-ex/0309016 “We are forced to conclude, that appearance of this peak does not correspond to any decay line in this energy range and is not connected with statistics, and cannot be considered as any evidence of neutrinoless double beta-decay.” “an ‘evidence’ of 2039 keV peak could be seen the 3d and 5th detectors’ data and only in the runs with under threshold pulses; all other runs of 4 assembled detectors (70% of statistics) do not give any evidence of 2039 keV peak.” t1/20n 1.55  1025y (90% CL)

  16. New 76Ge-DBD initiative @ MPIK H. Heusser, W. Hofmann, K.T. Knoepfle, S. Schönert, B. Schwingenheuer, H. Simgen MPIK • is convinced that DBD search with 76Ge is an interesting opportunity to be further pursued; • has a unique know-how in low-energy low-background physics (Gallex/GNO, Borexino, Lens, HP-Germanium, low-level chemistry) ; • considers the operation of ‘naked’ Ge-detectors in liquid nitrogen (G. Heusser, Ann. Rev. Nucl. Part. Sci 1995) a promising concept for background reduction; • considers the proposed experimental concept GENIUS (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)a good idea; • realizes that a new initiative with a new leadership is required since a long term commitment as well as an international cooperation is needed; • is convinced that the experimental efforts should be integrated within the EU DBD activities (ILIAS-IDEA).

  17. 100 mee (eV) next step (~100 kg 76Ge) 10-1 6 ·10-2 (kg y keV) -1 10-3 (kg y keV) -1 10-2 10-4 (kg y keV) -1 10-5 (kg y keV) -1 101 102 103 104 100 MT (kg y) Improving the sensitivity Sensitivity: mee (b DE / M T)1/4 HdM HdM (H.V. Klapdor-Kleingrothaus et al., (HEIDELBERG-MOSCOW Collaboration), Eur. Phys. J. A 12 (2001) 147): M·T = 35.5 kg y b = 6 ·10-2 (kg y keV) -1 DE ~ 4.2 keV.

  18. 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

  19. Work in progress • Critical assessment of Ge-76 DBD potential (MC studies internal /external backgrounds) • Project study how to accommodate large LN (LAr) facility @ LNGS  goal: reduction of size while retaining shielding performance • Preparation of germanium in LN/LAr @ MPIK low-level lab  operational test of long-term stability • Tests of alternative electrical contact methods  reduction materials close to crystal (bgd. reduc.) • Study of a new method to suppress backgrounds • Critical assessment of Ge-76 DBD potential (MC studies internal /external backgrounds) • Project study how to accommodate large LN (LAr) facility @ LNGS  goal: reduction of size while retaining shielding performance • Preparation of germanium in LN/LAr @ MPIK low-level lab  operational test of long-term stability • Tests of alternative electrical contact methods  reduction materials close to crystal (bgd. reduc.) • Study of a new method to suppress backgrounds

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

  21. Space @ LNGS ~14 m 14.80 m

  22. Solving the space problem (a) new tank design study: vacuum + super-insulating foils (engineering study being completed)

  23. Solving the space problem (b) • Lead layer submersed in LN • 232Th activity of lead  tank Ø • Ongoing: measurement of new lead from JL Goslar. Preliminary results ~30Bq/kg Preliminary dimensions: Inner Ø: 6.5 m lead layer: 0.3 m (~700 t) Outer Ø: 9.8 m

  24. Solving the space problem (c) 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 Version (a):  Ø of sphere: ~10 m (1.5 m for crystal array) Version (b)  minimal distance lead-crystal: ~1.5 m  inner-Ø: 4.5 m (1.5 m for crystal array),  outer-Ø: ~ 8 m

  25. Scintillation of LAr – opportunity for an active shielding system • Scintillation yield: 40,000 photons / MeV (4 x organic liquid scintillator) • Emission in XUV (~130 nm) • Wavelength shifting required • with Xe addition (178 nm), tested by ICARUS • with organic WLS (ongoing DESY-Zeuthen/MPIK project) • Challenge: Ar-39, Ar-42 (mainly for DM)

  26. 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]

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

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

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

  30. 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

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

  32. Common approach to large Ge DBD Experiment Integration with EU & US activities • MPIK activities integrated in ILIAS EU-DBD network and joint research projects • Most likely only one Ge experiment worldwide • Contacts with Majorana established

  33. 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 • New Ge-76 DBD initiative at MPIK • Re-evaluate shielding options; design tank; contact with LNGS established to define technical specs. • Prepare setup for long-term tests of Ge in LN2 /LAr at MPIK • Investigate detector options with manufacturers & lab tests • look for collaborators

  34. Summary and outlook (2) • 1-year time scale • Proposal for full-scale LN2 / LAr facility for Gran Sasso • 2-3 year time scale: build & operate facility • Background studies (& DM search) with natural Ge • DBD physics run with first 76Ge samples (~20 kg) • Upgrade 100 kg (  5M Euro) • Converge towards full-scale experiment with a sensitivity of mee~10 meV

  35. Backup

  36. Sources in NEMO3 detector (20 sectors) Frejus Underground Laboratory (4800 m.w.e.) bb source foils (thickness ~ 60 mg/cm2) Study of 2 process 116Cd (0.40 kg) Qbb= 2802 keV 130Te (0.45 kg) Qbb= 2533 keV 150Nd (36.5 g) Qbb= 3367 keV 96Zr (9.43 g) Qbb= 3350 keV 48Ca (6.99 g) Qbb= 4271 keV natTe (0.61 kg) Background study Cu (0.62 kg) 82Se (0.93 kg) Qbb = 2995 keV 100Mo (6.9 kg) Qbb = 3034 keV Study of 0 and 2 process

  37. Future of “à la NEMO” NEMO3, Phase-2: 10 kg of 82Se or even better: 10 kg of 150Nd D.O.E. starts purification of Se and Nd (INEEL, Idaho Falls, USA) 10 kg 150Nd, 5 years of data: <mn> < 0.06 – 0.3 eV • Next step would be 100 kg enriched source: 100Mo (or 82Se or 150Nd) • Background rejection: • NEMO3 after 1 year of data will validate 208Tl and 214Bi purification processes • and neutron rejection at the level required for 100 kg of 100Mo • Need to improve Energy Resolution to separate bb0n and bb2n • We need FWHM ~ 8%/E (MeV) (instead of 14% for NEMO-3) • in order to have ~ 1 event/year of bb2n in the bb0n energy window (like for NEMO3) • How to improveDE/E ? • calorimeter: Silicium (e-) + small scintillator (g) ? • Modular source: bkg rejection + energy loss improvement • Need to increase the bb0n efficiency • Energy resolution • Geometrical acceptance • Energy loss of electrons 4 modules e = 60 mg/cm2 But NEMO collaboration is now working with first NEMO3 data… Wait and see !… (C. Augier, ECT)

  38. SUMMARY

  39. 2P1/2 650 nm 493 nm metastable (47 s) 4D3/2 2S1/2 EXO (136Xe) : Enriched Xenon Observatory Phys. Lett., B480, 12 (2000) Univ. of Alabama, Caltech, IBM Almaden, UC Irvine, ITEP Moscow, Neuchatel, Stanford, Torino, Trieste Up to 10 tons of 80% enriched 136Xe (world production ~30 tons/year) Detect the 136Ba+ daughter ion correlated with the bb decay (136Xe g136Ba++ e- e-)using optical spectroscopy (Moe, Phys. Rev. C44, 931, 1991) Should eliminate all backgrounds except bb2n Possible real time optical detection if the ion is localized and probed with laser Single ions can be detected from a photon rate of 107/s Expected sensitivity:

  40. Both Liquid Xe and Gas Xe options open • Advantage of TPC Gas Xe: • Information from tracking • can resolve 2 blobs • Can optically detect the Ba+ in-situ • Advantages of Liquid Xe: • very small detector (3m3 for 10 tons) • No high pressure • Ba++ neutralization easier • Unknowns for Liquid Xe: • Is energy resolution sufficient ? • Ba extraction with good efficiency ? • (via a cold finger electrode coated in frozen Xe) First 100 kg test production completed in April 2002 Caltech-Neuchâtel-PSI, Gotthard und.lab. (3000 mwe) TPC, 62.5 % enriched 236Xe at 5 bar (180 l fiducial, 5.3 kg) E0=2.48 MeV High pressure (5 bars) 1t Xe gas TPC with laser tagging Energy Resolution obtained by Gotthard 5 bar xenon : s(E)/E= 2.7 % at 2.48 MeV for electrons (232Th) Some R&D to improve energy resolution and efficiency Micromegas Readout to amplify charge Light detection (electroluminescence) in xenon (+ CF4 ?) • Ba ion is electrostatically attracted to the cold finger • Later the cold finger can be heated to evaporate the Xe and release the Ba ion into a radio frequency quadrupole trap. • Then the Ba+ is optically detected. First test of L-Xe ionization chamber (1 liter) to test energy resolution: Good acceptance to scintillation AND ionization Best resolution obtained by linear combination of the scintillation and ionization signals Resolution ~ 2%, sufficient for EXO experiment Test UHV/High Pressure Ba ion trap: initial test successful Initial prototype with 200 kg enriched Xe without Ba tagging will operate at the Waste Isolation Pilot Plant (WIPP, New Mexico)

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