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K. Zuber, Univ. of Sussex

K. Zuber, Univ. of Sussex. Epiphany Conference Cracow, 5-7 Jan. 2006. Neutrinoless double beta decay experiments. Contents. Double beta decay and neutrino masses Experimental status Future activities Outlook and summary. Beta and double beta decay. Beta decay. -.

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K. Zuber, Univ. of Sussex

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  1. K. Zuber, Univ. of Sussex Epiphany Conference Cracow, 5-7 Jan. 2006 Neutrinoless double beta decay experiments

  2. Contents • Double beta decay and neutrino masses • Experimental status • Future activities • Outlook and summary

  3. Beta and double beta decay Beta decay - • (A,Z)  (A,Z+1) + e- + e-decay - • n  p + e- + e Double beta decay - • (A,Z)  (A,Z+2) +2 e- + 2e2 • (A,Z)  (A,Z+2) + 2 e-0 changing Z by two units while leaving A constant 0: Only possible if neutrinos are Majorana particles In nature there are 35 isotopes 2: Seen in 12 isotopes, important for nuclear physics input

  4. Neutrino mass schemes • almost degenerate neutrinos m1≈ m2≈ m3 • hierarchical neutrino mass schemes normal inverted

  5. 3 Flavour oscillations (PMNS) Analogous to CKM matrix solar atmospheric If sin 13 0 CP-violation Majorana: U= UPMNS diag(1,e i ,e i )

  6. Physical quantities Experimental observable: Half-life Double beta decay: Effective Majorana neutrino mass relative CP phases = 1 Beta decay me =  |Uek|2 mk

  7. Neutrino mass schemes and DBD „normal“ mass hierarchy m1<m2<m3 „inverted“ mass hierarchy m3 < m1 < m2 almost degenerate neutrinos m1≈ m2≈ m3 Benchmark number to discriminate betweenhierarchical models: m = 50 meV

  8. ++ -modes n p e In general: Double charged higgs bosons, R-parity violating SUSY couplings, leptoquarks... e p n Q-4mec2 • (A,Z)  (A,Z-2) + 2 e+ (+2e) ++ Q-2mec2 • e- + (A,Z)  (A,Z-2) + e+ (+2e )+/EC Q • 2 e- + (A,Z)  (A,Z-2) (+2e) EC/EC Important to reveal mechanism if 0 is discovered Enhanced sensitivity to right handed weak currents (V+A)

  9. Neutrino mass vs. right handed currents <> EC/ß+ Possible evidence <m>(eV) M. Hirsch et al., Z. Phys. A 347,151 (1994)

  10. Rp violating SUSY Double beta probes

  11. Contents • Double beta decay and neutrino masses • Experimental status • Future activities • Outlook and summary

  12. m O-O A Even E-E      Z Zo Requirements Weizsäcker formula for A=const near minimum well approximated by Pairing energy  leads to splitting:  = 0 for even-odd, odd-even  = - 12 MeV/A1/2 for even-even = + 12 MeV/A1/2 for odd-odd ++ There are 35 --isotopes in nature

  13. Example - Ge76

  14. Ca 48 4271 0.187 4.10E24 2.52E16 Ge 76 2039 7.8 4.09E25 7.66E18 Se 82 2995 9.2 9.27E24 2.30E17 Zr 96 3350 2.8 4.46E24 5.19E16 Mo 100 3034 9.6 5.70E24 1.06E17 Pd 110 2013 11.8 1.86E25 2.51E18 Cd 116 2802 7.5 5.28E24 1.25E17 Sn 124 2288 5.64 9.48E24 5.93E17 Te 130 2529 34.5 5.89E24 2.08E17 Xe 136 2479 8.9 5.52E24 2.07E17 Nd 150 3367 5.6 1.25E24 8.41E15 Phase space 0nbb decay rate scales with Q5 2nbb decay rate scales with Q11 Q-value (keV) (PS 0v)–1 (yrs x eV2) (PS 2v) –1 (yrs) Isotope Nat. abund. (%)

  15. Spectral shapes 0: Peak at Q-value of nuclear transition Measured quantity: Half-life Dependencies (BG limited) T1/2  a •  (M•t/E•B)1/2 link to neutrino mass 1 / T1/2= PS * ME2 * (m / me)2 Sum energy spectrum of both electrons Nuclear physics input needed !

  16. Nuclear matrix elements measured quantity quantity of interest 1 / T1/2 = PS * NME2 * (m / me)2 The big unknown Started worldwide effort for a coherentprogram to reduce NME uncertainty down to 30%, summary report available nucl-ex/0511009 Needs international coherent effort http://www.ippp.dur.ac.uk/0NU2B/2005.html

  17. Nuclear matrix elements 1 / T1/2= PS * ME2 * (m / me)2 charge exchange(n,p), (d,2He) charge exchange(p,n), (3He,t) muon capture nu N scattering 1+ beta- decays (A,Z+1) EC/beta+ decays antineutrino-capture 0+ (A,Z) Q - values 0+ (A,Z+2) Theory: Shopping list what to measure to improve calculations Experiment: Where can it be measured, who? Follow up workshop held at Osaka, Dec. 2005 , NNR 05

  18. Outcome: Working packages • Working package 1: Charge exchange reactions • Working package 2: Q-value measurements • Working package 3: Muon capture • Working package 4: Double electron capture • Working package 5: Neutrino nucleus scattering • Working package 6: Nucleon transfer reaction Urgency: Some facilities might vanish in the near future!!!

  19. Double beta transitions All even-even ground state transitions are 0+ 0+ Fermi‘sGolden rule 2: Only Gamow-Teller transitions

  20. Charge exchange reactions 2: Only intermediate 1+ states contribute Supportive measurementsfrom accelerators Done for Ca-48 and Cd-116 and some other systems, all needed Currently: (d,2He) and (3He,t)

  21. The dominant problem - Background How to measure half-lives beyond 1020 years??? • The usual suspects (U, Th nat. decay chains) • Alphas, Betas, Gammas • Cosmogenics • thermal neutrons • High energy neutrons from muon interactions • 2

  22. Heidelberg -Moscow • Five Ge Diodes (mass 10.9 kg) • Isotopical enriched ( 86%) in 76Ge • lead shield and nitrogen purgingPeak at 2039 keV H.V. Klapdor-Kleingrothaus et al, Europ. Phys. J. A 12, 147 (2001) T1/2 > 1.9 x 1025 yr (90% CL) m < 0.35 eV Evidence ? Subgroup of collaboration T1/2 = 0.6 - 8.4 x 1025 yr m = 0.17 - 0.63 eV H.V. Klapdor-Kleingrothaus et al, Phys. Lett. B 586, 198 (2004)

  23. Heat sink Thermometer Double beta decay Crystal absorber CUORICINO/CUORE - Principle Thermal coupling example: 750 g of TeO2 @ 10 mKC ~ T 3(Debye) C ~ 2 x10-9 J/K1 MeVg-ray DT ~ 80 mKDU ~10 eV

  24. CUORICINO - Results about 40 kg running 208Tl 60Co sum 130Te DBD T1/2 > 1.8 x 1024 yrs (90% CL) m < 0.2-1.1 eV C.Arnaboldi et al, hep-ex0501034, Phys. Rev. Lett. 2005 Idea: CUORE (750 kg) approved by INFN

  25. NEMO-III Only approach with source different from detector 100Mo6.914 kg Qbb = 3034 keV 82Se0.932 kg Qbb = 2995 keV

  26. Data • Data 22 Monte Carlo 22 Monte Carlo Background subtracted Background subtracted 100Mo results 7.37 kg.y (Data Feb. 2003 – Dec. 2004) Angular Distribution Sum Energy Spectrum 219 000 events 6914 g 389 days S/B = 40 219 000 events 6914 g 389 days S/B = 40 NEMO-3 NEMO-3 100Mo 100Mo E1 + E2 (keV) Cos() 2: T1/2 = 7.14 ± 0.02 (stat) ± 0.54 (syst)  1018 y 0: T1/2 > 3.1 x 1023 yrs (90% CL) m < 0.7 - 2.8 eV Idea: Super-NEMO (100 kg) R. Arnold et al, hep-ex/0507083

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

  28. + further interested institutes Cobra - The people D. Dobos, C. Gößling, H. Kiel, D. Münstermann, S. Oehl, T. Villett University of Dortmund J. Dawson, C. Montag, D. Palzaird, C. Reeve, J. Wilson, K. Zuber University of Sussex P.F. Harrison, B. Morgan, Y. Ramachers, D. Stewart University of Warwick A. Boston, P. Nolan University of Liverpool S. Fox, B. Fulton, A. Smith, R. Wadsworth University of York T. Bloxham, M. Freer University of Birmingham P. Seller Rutherford Appleton Laboratory M. Junker Laboratori Nazionali del Gran Sasso

  29. Isotopes nat. ab. (%) Q (keV) Decay mode

  30. Advantages • Source = detector • Semiconductor (Good energy resolution, clean) • Room temperature (safety) • Modular design (Coincidences) • Two isotopes at once • Industrial development of CdTe detectors • 116Cd above 2.614 MeV • Tracking („Solid state TPC“)

  31. 2 - decay 2 is ultimate, irreducible background Energy resolution important semiconductor Fraction of 2 in 0  peak: S. Elliott, P. Vogel, Ann. Rev. Nucl. Part. Sci. 2002 Signal/Background: + Tracking option

  32. The 2x2 prototype Setup installed at Gran Sasso Underground Laboratory 4 naked 1cm3 CdZnTe more than 3.8 kg x days of data

  33. Physics - 113Cd 113Cd one of only three 4-fold forbidden -emitters known in nature T1/2 = (8.2 ± 0.2 (stat.) +0.2-1.0 (sys)) 1015 yrs C. Goessling et al., nucl-ex/0508016, acc. by Phys. Rev. C

  34. First results H.Kiel, D. Münstermann, K. Zuber, Nucl. Phys. A 723,499 (2003) 0 NPA 723 COBRA EC-modes NPA723 COBRA T1/2 close to 1020 years obtained Current results are preliminary 64Zn limits world best

  35. Coincidences Aim: Coincidences among crystals should significantly reduce gamma background 2614 keV gamma (MC) About 0.2 % ofevents are coincidences Array too small to prove power of coincidences  Larger Array

  36. The 64 detector array Aim for next 2 years: The next step towards a large scale experiment, Scalable modular design, explore coincidences Mass is factor 16 higher, about 0.5 kg CdZnTe Include: CoolingNitrogen flushing • Physics: • - Can access • 2ECEC in theoreticallypredicted region • Precision measurement of 113Cd • - New limits Detectors are at Dortmund, LNGS spring 06

  37. The solid state TPC Introduce tracking properties by using segmented or pixellated electrodes and pulse shape analysis Single electron spectra Angular correlation coefficient 

  38. Pixellated detectors Solid state TPC 3D - Pixelisation:

  39. Nobody said it was going to be easy, and nobody was right George W. Bush

  40. Join the Party!

  41. Contents • Double beta decay and neutrino masses • Experimental status • Future activities • Outlook and summary

  42. Back of the envelope T1/2 = ln2 • a•NA• M • t / N (tT) ( Background free) 50 meV implies half-life measurements of 1026-27 yrs 1 event/yr you need 1026-27 source atoms This is about 1000 moles of isotope, implying 100 kg Now you only can loose: nat. abundance, efficiency, background, ...

  43. Future projects small scale ones will expand, very likely not a complete list...

  44. Sensitivity 50 meV Dimension it right! Current idea: 40x40x40 CdZnTe detectors = 420 kg, enriched in 116Cd

  45. EXO New feature: Tracking and scintillation 136Xe 136Ba++ e- e- final state can be identified using optical spectroscopy (M.Moe PRC44 (1991) 931) 200 kg enriched Xe prototype under construction at WIPP

  46. L=2 Processes In general 9 mass terms • e-conversion on nuclei • M. Flanz, W. Rodejohann, K. Zuber, Eur. Phys. J. C 16, 453 (2001) W. Rodejohann, K. Zuber,Phys. Rev. D 63, 054031 (2001) • limits on <m> (in GeV) K. Zuber, Phys. Lett. B 479,33 (2000) • M. Flanz, W. Rodejohann, K. Zuber,Phys. Lett. B 473, 324 (2000) W. Rodejohann, K. Zuber,Phys. Rev. D 62, 094017 (2000) Limits are unphysical

  47. Candidate events H1 charged current event NOMAD trimuon event

  48. Summary Double beta decay is the gold plated channel to probethe fundamental character of neutrinos Taking current evidences from oscillation data it islikely to be the only way to fix the absolute neutrino mass To go below 50 meV requires hundreds of kilograms ofenriched material However, there is a hotly disputed evidence by the Heidelberg group, which would imply almost degenerate neutrinos To account for matrix element uncertainties supportivemeasurements are considered and in addition todisentangle the physics mechanism we need at least 3(4) isotopes measured

  49. Hope....

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