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Exploring Nuclear Matrix Elements in Double Beta Decay

This lecture discusses the general introduction to double beta decay (DBD), neutrino oscillations and other physics related to DBD, the importance of nuclear matrix elements, and the experimental considerations and current status of DBD experiments.

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Exploring Nuclear Matrix Elements in Double Beta Decay

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  1. Contents Lecture 1 • General introduction • What is measured in DBD ? • Neutrino oscillations and DBD • Other BSM physics and DBD • Nuclear matrix elements Lecture 2 • Experimental considerations • Current status of experiments • Future activities • Outlook and summary

  2. Nuclear matrix elements The dark side of double beta decay

  3. Nuclear matrix elements F. Simkovic

  4. Uncertainties F. Simkovic

  5. Uncertainties F. Simkovic

  6. Reminder 2 0

  7. Multipoles 0: All intermediate states contribute How to explore those???

  8. Charge exchange reactions 2: Only intermediate 1+ states contribute Supportive measurementsfrom accelerators Currently: (d,2He) and (3He,t)

  9. M0 calculations V. Rodin, A. Faessler, F. Simkovic, P. Vogel, nucl-th/0503063 Remember: Half life to neutrino mass conversion is proportional to M2 Consequence: We have to measure 3-4 isotopes to compensate for that Looks convincing, but not everybody agrees...

  10. Summary - So far • Neutrinoless double beta decay is the gold plated channel to probe the Majorana character of neutrinos • It also provides information on the absolute neutrino mass scale • Benchmark of 50 meV, hierarchies hard to disentangle, probably only way of laboratory experiment to go to 50 meV (ignoring claimed evidence) • If observed, Schechter-Valle theorem guarantees Majorana neutrinos • A lot of physics can be deduced not accessible to accelerators, but how to disentangle contributions to 0 • However there are also major uncertainties, especially nuclear matrix elements • We have achieved quite a lot, but there is still a lot to do

  11. Can you prove that  is Dirac? Answer: Show that neutrinos have a static magnetic momentt Energy in field: CPT changes sign of spin, thus Eem=-Eem, bu they must be theesame for Majorana neutrinos. Hence

  12. Contents Lecture 1 • General introduction • What is measured in DBD ? • Neutrino oscillations and DBD • Other BSM physics and DBD • Nuclear matrix elements Lecture 2 • Experimental considerations • Current status of experiments • Future activities • Outlook and summary

  13. The search for 0 or

  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. Back of the envelope T1/2 = ln2 • a•NA• M • t / N (tT) ( Background free) For half-life measurements of 1024-25 yrs 1 event/yr you need 1024-25 source atoms This is about 10 moles of isotope, implying 1 kg Now you only can loose: nat. abundance, efficiency, background, ...

  16. 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

  17. Half - life estimate 0 T1/2 = ln2 • a•NA• M • t / N (tT) Signal sensitivity  stat. precision of background Nobs = NBG Background  detector mass T1/2  a •  (M•t/E•B)1/2 • a: isotopical abundance B • M: mass • t: measuring time • E: energy resolution E Q-E/2 Q Q+E/2 • B: background (c/keV/kg/yr)

  18. Signal information (A,Z)  (A,Z+2) + 2 e- Signal: One new isotope (ionised), two electrons (fixed total energy) Single electron energies Angle between electrons Sum energy of both electrons Daughter ion (A,Z+2) Gamma rays (eg. four 511 keV photons in ++)

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

  20. Contents Lecture 1 • General introduction • What is measured in DBD ? • Neutrino oscillations and DBD • Other BSM physics and DBD • Nuclear matrix elements Lecture 2 • Experimental considerations • Current status of experiments • Future activities • Outlook and summary

  21. Geochemical approach Major advantage: Experiment is running since a billion years Signal: Isotopical anomaly T: age of ore Practically search has been possible due to the high sensitivity ofnoble gas mass spectrometry. Thus daughter should be noble gas.  82Se, 128,130Te Disadvantage:You cannot discriminate2 from 0 T. Kirsten et al, PRL 20 (1968)

  22. Experimental techniques Source = detector Source  detector Semiconductors Time projection chambers (TPC) Heidelberg-Moscow, IGEX, COBRA, GERDA, MAJORANA NEMO-3, SuperNEMO,DCBA, EXO Cryogenic bolometers CUORICINO, CUORE Scintillators SNO+, CANDLES, MOON,GSO, XMASS

  23. Heidelberg -Moscow • Five Ge diodes (overall mass 10.9 kg) • isotopically enriched ( 86%) in 76Ge • Lead box and nitrogen flushing of the detectors • Digital Pulse ShapeAnalysis Peak at 2039 keV

  24. Spectrum 0 peak region

  25. Latest HD-Moscow results Statistical significance: 54.98 kg x yr Including pulse shape analysis: 35.5 kg x yr (installed Nov. 95, only 4 detectors) SSE T1/2 > 1.9 x 1025 yr (90% CL) m < 0.35 eV

  26. Evidence for 0-decay?- References Latest Heidelberg-Moscow results H.V. Klapdor-Kleingrothaus et al., Eur. Phys. J. A 12,147 (2001) Evidence H.V. Klapdor-Kleingrothaus et al., Mod. Phys. Lett. A 16,2409 (2001) Critical comments F. Feruglio et al., hep-ph/0201291 C.A. Aalseth et al., hep-ex/0202018 Reply H.V. Klapdor-Kleingrothaus, hep-ph/0205228 H.L. Harney, hep-ph/0205293 New evidence H.V. Klapdor-Kleingrothaus et al., Phys. Lett. B 586,198 (2004)

  27. Heidelberg -Moscow more statistics Recalibration T1/2 = 0.6 - 8.4 x 1025 yr Subgroup of collaboration m = 0.17 - 0.63 eV H.V. Klapdor-Kleingrothaus et al, Phys. Lett. B 586, 198 (2004)

  28. The peak... 1.) Is there a peak? Statistical treatment (Bayesian) 2.) If it is real, is it something specific to Ge? 56Co produced by cosmic rays (2034 keV photon+ 6 keV X-ray) 76Ge(n,)77Ge (2038 keV photon) Some unknown line Inelastic neutron scattering (n,n‘) on lead Other suggestions, can be combination of all Note: We are talking about 1 event/year The easiest person to fool is yourself (R. Feynman)

  29.  Check with a different isotope Uncertainties in nuclear matrix elements, example 116Cd <m>=0.4eV V. Rodin et al.,nucl-th/0503063, Nucl. Phys. A 2006

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

  31. 0nDBD Gamma region, dominated by gamma and beta events, highest gamma line = 2615 keV 208Tl line (from 232Th chain) Alpha region, dominated by alpha peaks (internalorsurfacecontaminations) CUORICINO - Spectrum

  32. CUORICINO - Results about 40 kg running 208Tl 60Co sum 130Te DBD T1/2 > 2.4 x 1024 yrs (90% CL) m < 0.2-1.1 eV

  33. CUORICINO-CUORE 19 towers 13x4 crystals/tower Future: CUORE 760 kg TeO2 approved

  34. NEMO-3 Only approach with source different from detector

  35. bb2n measurement bb0n search bb decay isotopes in NEMO-3 detector 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

  36. NEMO-III - Event Typical 2 event of 100Mo

  37. 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 = 7.11 ± 0.02 (stat) ± 0.54 (syst)  1018 y 0: T1/2 > 5.8 x 1023 yrs (90% CL) m < 0.6 - 2.8 eV Idea: SuperNEMO (100 kg) R. Arnold et al, PRL 95 (2005)

  38. source tracker calorimeter 1 m 4 m 5 m Top view Side view SuperNEMO Idea: Use 100 kg enriched 82Se

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

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

  41. 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“)

  42. 2 - decay 2 is ultimate, irreducible background Energy resolution extremely important check whether people use FWHM or  (there is a factor 2.35 difference) Fraction of 2 in 0 peak: S. Elliott, P. Vogel, Ann. Rev. Nucl. Part. Sci. 2002 Signal/Background:

  43. The first layer 4x4x4 detector array = 0.42 kg CdZnTe semiconductors Installed at LNGS about three month ago

  44. The solid state TPC Energy resolution Tracking • Massive background • Reduction (Particle-ID) • Positive signal information Pixellated CdZnTe detectors

  45. Pixellisation - I = 1 pixel,  and = several connected pixel, = some disconnected p. • Particle ID possible, 200m pixels (example simulations): • eg. Could achieve nearly 100% identification of 214Bi events (214Bi  214Po  210Pb) . 3 MeV  0  ~15m 1-1.5mm Beta withendpoint 3.3MeV 7.7MeV  life-time = 164.3s

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

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

  48. Contents Lecture 1 • General introduction • What is measured in DBD ? • Neutrino oscillations and DBD • Other BSM physics and DBD • Nuclear matrix elements Lecture 2 • Experimental considerations • Current status of experiments • Future activities • Outlook and summary

  49. 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, ...

  50. Future projects, ideas Status 2006 small scale ones will expand, very likely not a complete list...

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