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Experiments on Neutrino Nature and Mass

Experiments on Neutrino Nature and Mass. Challenges for Non-accelerator Neutrino Physics Experiments Y. Ramachers, University of Warwick. Outline. How to weigh neutrinos Current Experiments: an Overview Next-generation proposals Summary of merits and challenges. How to weigh neutrinos?.

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Experiments on Neutrino Nature and Mass

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  1. Experiments on Neutrino Nature and Mass Challenges for Non-accelerator Neutrino Physics Experiments Y. Ramachers, University of Warwick Y. Ramachers

  2. Outline • How to weigh neutrinos • Current Experiments: an Overview • Next-generation proposals • Summary of merits and challenges Y. Ramachers

  3. How to weigh neutrinos? • Neutrino Oscillations (see talks from yesterday: B. Kayser, Th. Schwetz, G. Ross and B. Scott) • Cosmology (see following talk: S. King) • Direct Beta Decay Endpoint • Double Beta Decay Y. Ramachers

  4. Single and Double Beta Decay – fundamentally different playing fields Y. Ramachers

  5. Single and Double Beta Decay – fundamentally different playing fields Single Beta Decay: Double Beta Decay: Y. Ramachers

  6. Single Beta Decay Two complimentary experimental approaches Charge Spectrometer: KATRIN Calorimeter: MARE • Source: Tritium, Q-value 18.6 keV • Filter electron energies • Count electron events above filter threshold • Energy resolution target: 0.93 eV • Mature technology: Mainz/Troitsk limit achieved 2.2 eV • Sensitivity target: 0.2 eV • http://www-ik.fzk.de/~katrin/index.html • Source: Rhenium-187, Q-value 2.5keV • Source = Detector: Cryogenic micro-calorimeter • Energy resolution: 10-20 eV • Mature technology: TES thermometry Sensitivity target: Test Mainz/Troitsk 2.2 eV • Long-term: MARE-2, 0.2 eV • http://mare.dfm.uninsubria.it/ Y. Ramachers

  7.  (Q – Ee)  (Q – Ee)2 – Mn2c4 (Q – Ee)2 3 |ne = SUei |nMi  i=1 K(Ee) dN [1 + dR(Z,Ee)] (Ee+mec2) (Q – Ee)2 F(Z,Ee) S(Ee)  GF2 |Mif|2 Q – M3 dE Q – M2 Q – M1 K(Ee) Q Ee Ee Anything beyond 0.2 eV ? Motivation for new ideas A. Giuliani, PIC2005, Prague + Cosmic neutrino background detection, see M. Blennow and ref. therein, astro-ph/0803.3762 Y. Ramachers

  8. Double Beta Decay: Double Beta Decay 2nbb Experimental signature Allowed and observed 0nbb Forbidden – Interesting ! Neutrinos must be massive Majorana particles Y. Ramachers

  9. Experimental Techniques A. Nucciotti, IDM2004, Edinburgh Y. Ramachers

  10. Success and further improvements: HowTo’s On the way to 100meV: Missing factor 2-5 gained by • 16-625 fold increase in exposure (Mt) and/or • 16-625 fold reduction of background, B On the way to 10meV : Extrapolate existing experiments over 5-6 orders of magnitude !!! Not at all hopeless, but a challenge ! Y. Ramachers

  11. Counts [a.u.] Counts [a.u.] Electron sum energy/Q-value HowTo 2 Energy resolution and Irreducible background (2nbb) • Need good DE • Need good e • Need high enrichment, a • Measurement time limited • Background and Mass count most Choose appropriate detector technology (e, DE, a, t, cost for M) and work on B ! Y. Ramachers

  12. 0nbb experiments overview 0nbb experiments overview from R. Saakyan, SLAC Exp. Seminar, Jan. 2008 * Matrix elements from MEDEX’07 or provided by experiments Y. Ramachers

  13. Heidelberg-Moscow Exp. 5 high-purity germanium detectors, enriched in 76Ge Total active mass: 10.96 kg, total exposure: 71.7 kg years Main background from U/Th in the set-up: 0.11 c/(keV kg y) at Qbb H.V. Klapdor-Kleingrothaus et al., NIM A522 (2004) 371 Y. Ramachers

  14. Heidelberg-Moscow Exp. Evidence peak Full data set: 71.7 kg years After pulse-shape analysis: 51.4 kg years A peak at 2039 keV = Q-value for 0nbb No counter-argument brought forward anymore: Test evidence experimentally ! Y. Ramachers

  15. Comment on Gaussian peaks and low statistics Blind-analysis reveals the subtle challenge: Efficiency without human intervention GERDA Phase I testing evidence claim; 13 counts on 3 bkgr give efficiency for any(!) Fit: 17.4% HD-Mos. evidence: 28 counts on 10 bkgr efficiency for Fit: 18.7% Scan of total Signal and Background counts D.Y. Stewart and YR, to be submitted Y. Ramachers

  16. CUORICINO C. Arnaboldi et al., hep-ex/0802.3439 Cryogenic calorimeter, TeO2 crystals Operating Temp. about 10 mK 44 detector modules Total mass: 40.7 kg Y. Ramachers

  17. CUORICINO F. Ferroni, ICATTP, Villa Olmo, Oct. 2007 Y. Ramachers

  18. CUORICINO F. Ferroni, ICATTP, Villa Olmo, Oct. 2007 Y. Ramachers

  19. NEMO-3 R. Arnold et al., hep-ex/0410021 2nbb example event Tracking Detector: 6.9 kg 100Mo, 0.9 kg 82Se (for latest results) (1) Source foil(s); (2) calorimeter (scintillator); (3) PMT’s; (4) tracking volume Y. Ramachers

  20. Data until spring 2006 82Se 100Mo 693 days of data Phase I + Phase II T1/2 > 5.8 × 1023 y @ 90% C.L. mn < (0.8 – 1.3) eV [1-3] T1/2 > 2.1 × 1023 y @ 90% C.L. mn < (1.4 – 2.2) eV [1-3] Both simple counting and likelihood methods are consistent R. Saakyan, SLAC Exp. Seminar, Jan. 2008 NEMO-3 results 693 days of data Phase I + Phase II Y. Ramachers

  21. New Experiments: Example 1 SuperNEMO Next-generation tracking detector Planar geometry. 20 modules for 100+ kg Baseline design: Source: 40 mg/cm2; 12 m2 per module Readout total: ~ 40-60k geiger channels for tracking ~ 10-20k PMTs (3k if scintillator bars design) Single sub-module with ~5-7 kg of isotope R. Saakyan, SLAC Exp. Seminar, Jan. 2008 Y. Ramachers

  22. SuperNEMO NEMO-3 150Nd or 82Se isotope 100Mo isotope massM 100-200 kg 7 kg efficiency  ~ 30 % 8 % 208Tl mBq/kg if 82Se: 214Bi  10 mBq/kg 208Tl: < 20 mBq/kg 214Bi: < 300 mBq/kg internal contaminations 208Tl and 214Bi in the bb foil energy resolution (FWHM) 8% @ 3MeV 4%@ 3 MeV T1/2(bb0n) > 2 x 1024 y <mn> < 0.3 – 0.9 eV T1/2(bb0n) > (1-2) x 1026 y <mn> < 0.04 - 0.11 eV SuperNEMO Y. Ramachers

  23. SuperNEMO Design Study • Approved in UK, France and Spain. Smaller but vital contributions from US, Russia, Czech Republic, Japan. • Main tasks and deliverables • R&D on critical components • Calorimeter energy resolution of 4% at 3 MeV • Optimisation of tracking detector and construction (robot) • Better background rejection (e.g. extra veto counters) • Ultrapure source production and purity control • Simulations and geometry optimisation (B-field question). • Technical Design report • Experimental site selection (Frejus, Canfranc, Gran Sasso, Boulby) Y. Ramachers

  24. New Experiments: Example 2 GERDA Next-generation semiconductor detector 70 m3 liquid Argon Status April 2008 from report to LNGS SC: • Cryostat installed at LNGS • Phase I detectors pass stability tests in cryogenic liquid • Phase II detector production in preparation • Water tank construction to follow • Clean room construction in October • Kai Zuber, TU Dresden, joined collaboration Cryostat 6 cm copper shield Ge Detector Array Y. Ramachers

  25. GERDA Y. Ramachers

  26. M, a: e: ΔE: B: Large enriched source, bulk (SNO++, EXO200) or modular Source = Detector Germanium semiconductor energy resolution (GERDA, CUORE) Ultra clean environment = embedded in active veto, self-shielding (GERDA, SNO++, EXO200) + Tracking (SuperNEMO) for background identification + extra-physics + best isotope, Nd-150 (SNO++, SuperNEMO) + daughter isotope identification in situ (EXO) A hypothetical bb-experiment: Cherry-picking for a second UK experiment All reviews agree on one point: There is no optimalbb-experiment! So, pick out what is good and compromise for a practical solution: A highly subjective procedure The impossible experiment, so - compromise Y. Ramachers

  27. A hypothetical bb-experiment: Compromises M, a: e: ΔE: B: Modular source Source = Detector Semiconductor energy resolution Ultra clean environment = embedded in active veto, self-shielding + Tracking, at least coarse + reasonable isotope, not covered yet – Cd-116 (b-b-) or Cd-106 (b+b+) - no daughter isotope identification Room-temperature version of GERDA – modified COBRA: CdZnTe semiconductors, pixel or strip-readout in liquid scintillator tank All necessary expertise present in the UK Y. Ramachers

  28. Conclusion I • Single Beta Decay can: • Measure the electron anti-neutrino mass directly, model-independent • Potentially gain access to more than one mass eigenstate and mixing matrix element • Potentially measure cosmic neutrino population • Double Beta Decay can: • Give access to the absolute mass scale • Reveal the particle nature • Evidence at 440 meV can ‘soon’ be tested independently(results maybe by 2010-2011) Y. Ramachers

  29. Conclusion II • The step to 100 meV sensitivity is a big step – current experiments will have to improve • The step to 10 meV is huge: All extrapolations (5-6 orders of magnitude) suffer from unknown background regime • Once upon a time: There was scope for a second UK double beta decay experiment – expertise and efforts still exist– point for discussion? • Not mentioned - beyond Mass and Nature: potentially reveal the physics mechanism for Lepton Number violation (tracking and/or matrix element measurement for many isotopes and double beta decay modes) and access CP-violation in the lepton sector together with single beta decay Y. Ramachers

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