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Neutrino Physics without Neutrinos An experimental overview of Double Beta Decay

Double Beta Decay, neutrino mass and BSM Physics Experimental techniques Physics sensitivity. Neutrino Physics without Neutrinos An experimental overview of Double Beta Decay. Ruben Saakyan University College London HEP 2012 Valparaiso, Chile 9 January 2012. Outline.

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Neutrino Physics without Neutrinos An experimental overview of Double Beta Decay

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  1. Double Beta Decay, neutrino mass and BSM Physics • Experimental techniques • Physics sensitivity Neutrino Physics without NeutrinosAn experimental overview of Double Beta Decay • Ruben Saakyan • University College London • HEP 2012 • Valparaiso, Chile • 9 January 2012 Outline

  2. Different from quark sector. Can CP-violation in lepton sector address matter-antimatter puzzle? Neutrinos are massive and they mix PMNS matrix Plots: Courtesy of MINOS collaboration 2

  3. Key Questions to Answer • Number of neutrinos: Are there sterile neutrinos? • θ13 (first hints from T2K and reactors?), • Precision values of mixing angles and Δm2 ’s • Absolute neutrino mass value. Only limits so far. • Tritium: Cosmology: • Neutrino mass spectrum: Normal (m1 < m2 < m3) • Inverted (m3 < m1 < m2) or Quasi-degenerate (m1≈m2≈m3)? • Origin of matter-antimatter asymmetry. • CP-violation in lepton sector: δ ≠ 0,π and/or α,β ≠ 0,π ? • Nature of Neutrinos: Majorana (ν = anti-ν) or Dirac (ν ≠ anti-ν)? • Full lepton number violation (required in • most Grand Unification Theories) . addressed by 0νββ decay

  4. Nature of Neutrinos: Majorana (ν = anti-ν) or Dirac (ν ≠ anti-ν)? ΔL ≠ 0 ΔL = 0 Directly related to fundamental symmetries of particle interactions Provides important information on origin of neutrino mass SEE-SAW To obtain m3~(Δm2atm)1/2, mD~mt, M3~1015GeV (GUT!) Lepton number violation is one of the key ingredients of leptogenesis as the mechanism to generate the baryon asymmetry of the Universe. More matter than anti-matter!

  5. Double Beta Decay in the Standard Model (Goeppert-Mayer, 1935) Recall pairing term in SEMF phase space odd-odd NME: Nasty Nuclear Matrix Element even-even M(A,Z) > M(A,Z+2) Qββ = M(A,Z) - M(A,Z+2) NME is measured in 2νββ • Second order process ⇒ rare (~1019-1021 yr) • Nevertheless observed for 11 nuclei • Experimental input for NME calculation

  6. (A, Z+2) (A, Z) Double Beta Decay Beyond the Standard Model Neutrinoless Double Beta Decay(Furry, 1939). ΔL = 2! NEW PHYSICS Lepton number violating parameter can be due to , V+A, Majoron, SUSY, H-- or a combination of them “Minimal” scenario - light Majorana mass Coherent sum over neutrino amplitudes

  7. Double Beta Decay. What is measured? (E1+E2)/Qββ

  8. Neutrinoless Double Beta Decay. Can we disentangle the underlying mechanism? V+A 〈mν〉 Majoron emission

  9. Double Beta Decay. Isotope Candidates. *J. Phys. G: Nucl. Part. Phys. 34 667 (2007) Over 40 nuclei can undergo ββ-decay (including β+β+ and 2K-capture) Only ~10 experimentally feasible more energetic decay : easier to separate from background • Isotope choice • Qββ • T1/2(2ν) (the longer the better) • Isotope abundance • Enrichment opportunities • NME - Input from 2ν measurements is useful • Phase space enrichment often possible, always expensive !

  10. 0νββ ??? 214Bi 214Bi KKDC Claim (76Ge) Degenerate unknown Inverted Hierarchy Effective Neutrino Mass (eV) Normal Hierarchy Klapdor et al. (KKDC) (2004) Lightest Neutrino Mass (eV) Majorana Mass Physics Reach Sensitivity Milestones “Immediate” Future: ~0.1 eV to check K-K claim Next step And then ~ 0.01 eV to cover I.H.

  11. Experimental Sensitivity maximise efficiency & isotope abundance maximise exposure = mass × time minimise background & energy resolution background limited background-free gets tedious pretty quickly …

  12. Only in North Hemisphere so far! Backgrounds. Cosmics. • Going underground is a must • ~106 reduction in cosmic muons • Spallation neutrons • γ’s, Rn and “environmental” neutrons depending on local geology

  13. 238U 4.5 billion-y 232Th 14 billion-y 208Pb stable 214Po 164 μs 208Tl 3.1 min 214Bi 20 min PROBLEM N(α,β) N(α,β) 222Rn 3.8 days PROBLEM N(α,β) N(α,β) 220Rn 55 sec Qβ= 3.27 MeV Qβ= 4.99 MeV GAS ! Backgrounds. Natural Radioactivity. • Primarily Uranium and Thorium decay chain products, present in all materials. • T1/2(232Th,238U) ~ 1010 years • T1/2(0νββ) > 1025 years • Neutrons from spontaneous fission and (αn)-reactions • What can be done ? • Extremely careful material selection. • Purification techniques. • Barriers against Radon penetration. • Background tagging/identification techniques.

  14. Backgrounds. Irreducible 2νββ. What can be done ? • Improve Energy Resolution • Choose isotope with long T1/2(2ν) • Precise measurement of 2νββspectral shape (characterise tails of the distribution)

  15. Experimental Approaches Tracking + Calorimetry. Source ≠ Detector (ala NEMO3 and SuperNEMO) Calorimeter-only. Source = Detector Main observable: Deposited energy Excellent ΔE/E High efficiency Relatively compact Some particle ID capability Full Topology Reconstruction Main limiting factor: background Strong background suppression and control “Smoking gun” 0νββ signature Sensitivity to different physics mechanisms of 0νββ Main limiting factor: efficiency HPGe, Bolometers, (Liquid)-Scintillators, LXe.

  16. We need Diversity A take-away message • We need to measure different isotopes with different experimental approaches • NME uncertainties • Tiny signal - Huge Background. Will you ever trust a single positive measurement? • Disentangle underlying physics mechanism

  17. ...and we have it! Disclaimer: I will only have time to go over a few examples to give a flavour of technologies. Apologies to projects I did not have time to go through.

  18. RESULTS

  19. Together with 2νββ of 76Ge these are the slowest decay processes ever observed! Results in 2011 NEMO-3 661 g of 130Te EXO-200 63 kg of 136Xe First ever measurement First direct measurement Phys. Rev. Lett. 107, 062504 (2011) Phys. Rev. Lett. 107, 212501 (2011) c.f. Indirect observations (geochemistry): - ~2.7 x 1021 yrs in 109 yr old rocks - ~8 x1020 yrs in 107-108 yr old rocks Indication from MIBETA c.f. in tension with previous DAMA-LXe result Physics Letters B 546 (2002) 23–28.

  20. Other recent (major) Results 0νββ 2νββ

  21. Steel cryostat with internal Cu shield High-purity liquid argon (LAr); shield & coolant. Future: active veto Water: γ, n shield; Cherenkov medium for μ veto • “Naked” enriched 76Ge(86%) detectors in LAr • Best way to directly check K-K claim (no NME uncertainties) • Excellent FWHM = 0.2% at Qββ • Phased Approach • Phase-I • 17.9kg of existing detectors (HM+IGEX) • Background goal: 0.01 cnts/(kg keV yr) - x20 smaller than H-M • Phase-II • Add new HPGe detectors - 40kg of 76Ge • Background goal: 0.001 cnts/(kg keV yr) • Phase-III • Join forces with Majorana project. 0.5-1t of 76Ge GERDA (Gran Sasso) Array of bare Ge-diodes HPGe diode Clean room Lock system GERDA Phase-I,II GERDA Phase-III

  22. GERDA Phase-I physics running started 1-Nov-11! • Initial problem with 42Ar is being dealt with • Average background in RoI ~ 0.04 cnts/(kg keV yr) • Phase-II detectors being made. LAr scintillation will be used

  23. Longitudinal View Transverse View Isotopes Large quantities: 100Mo (7kg) 82Se(1 kg) Small quantities: 116Cd 150Nd 48Ca 96Zr 130Te World’s most accurate measurements of T1/2(2ν) for these 7 isotopes Stopped data taking in Jan’11 to make room for SuperNEMO Tracker Volume source foil ββ vertex ββ vertex source foil B (25 G) scintillator PMT Scint. Hit Topological reconstruction of ββ-decay. NEMO-3 (LSM, Modane) • “Smoking gun” : complete event reconstruction for : • background rejection • signal characterisation (discovery!) <mv> < 0.31 – 0.96 eV

  24. SuperNEMO NEMO-3 82Se (or 150Nd or 48Ca) 100Mo 7 kg 100+ kg 208Tl: ~ 100 μBq/kg 214Bi: < 300 μBq/kg Rn: 5 mBq/m3 208Tl ≤ 2 μBq/kg 214Bi ≤ 10 μBq/kg Rn ≤ 0.15 mBq/m3 8% @ 3MeV 4% @ 3 MeV T1/2(ββ0ν) > 1÷2 x 1024 y <mν> < 0.3 – 0.9 eV T1/2(ββ0ν) > 1 x 1026 y <mν> < 0.04 - 0.1 eV From NEMO-3 to SuperNEMO R&D since 2006 Isotope Isotope mass M Contaminations in the ββ foil Rn in the tracker Calorimeter energy resolution (FWHM) Sensitivity

  25. SuperNEMO in planned LSM extension Full SuperNEMO 20 modules : 100 kg Start to probe I.H. Demonstrator Module Prove technology; reach “Klapdor” sensitivity Topological reconstruction of ββ-decay. SuperNEMO. Roadmap NEMO3 6-7 kg source foil 2000 tracker cells ~600 calorimeter channels SuperNEMO single module

  26. LSM underground lab extension (~2015) Modularity of SuperNEMO makes distributed location possible. ANDES??? LSM - January 2011 LSM - October 2011

  27. EXO - Enriched Xenon Observatory (136Xe) • Liquid Xe TPC • Easiest isotope to enrich • Energy measurement by ionisation and scintillation • FWHM = 3.8% at Qββ = 2.46 MeV • Self-shielding, particle ID capability • R&D on 136Ba+ tagging with lasers (136Xe→136Ba++ + 2e- +...) • Eventually 1-10t to reach 1027-1028 y ⇒ 10-70 meV EXO-200 at WIPP, New Mexico. • 175 kg of 136Xe • No Ba+ tagging • First measurement of 2νββ with 63 kg fiducial volume of 136Xe (see slide 19) • Understand operation of large LXe detector: backgrounds, resolution, Xe purification • 2 years: T1/2(0ν) > 6.4×1025 yr(90%CL)⇒ <mν> < 0.1-0.2 eV

  28. Loaded liquid scintillator SNO+ KamLAND-Zen SNO-Lab Canada Kamioka Japan • Isotope of choice 150Nd (Qββ = 3.4 MeV) • 0.1-0.3% load of natNd in ~800 ton of LS • 150Nd abundance = 5.6%. 0.3%⇒ 135 kg of 150Nd • Well-defined background model. “Source-in/Source-out” capability • Very stringent radiopurity requirements • < 10-17 g of U/Th per g of LS - demonstrated by Borexino • < 10-14 g of U/Th per g of Nd - very tough and to be demonstrated • Phase-I with natNd ~0.1 eV after 3 yr • If enrichment possible address I.H. in Phase-II/III • Intrinsically pure materials (Xe and LS) • Rapid progress • See Y. Efremenko talk for more

  29. Figure of Merit Phase-space factor normalised to 76Ge Normalised to exposure 500 kg yr and assuming the same NMEs Reliability of expected performance numbers is not taken into account

  30. O(100kg) generation will reach FOM ~4×1026 yr by 2018-2020. <mv> = 50-100 meV To exclude IH, i.e. to get 10-20 meV, we need FOM = ~1028 yr. Example: A 76Geexperiment even with ambitious b = 0.001 cnts/(kg keV yr) would need 30 tons (!) of enriched (!!) 76Ge measured over 5yr! Similar for other projects. Thus for 10 meV stage we have to find a “background-free” solution Example:150kg x 5 yrs of 48Ca, if no background and ε~40% , gives required FOM =1028 yr. NEMO3 had virtually no background in this region after 8 years of running! But we need to learn how to enrich 48Ca (0.19% nat. abundance) Ton-experiment, 10 meV and other speculations background-free background limited Future “Ton” experiments 222Rn poses serious challenge (How to control ~1atom/N×m3contamination?) Future may belong to “Big Three” 48Ca 4.27 MeV 96Zr 3.4 MeV 150Nd 3.4 MeV to break away from 222Rn progeny 214Bi 3.27 MeV

  31. The Roadmap Scenario 1 2015 2012 2020 Measurements with several isotopes. Possibility to disentangle LNV physics mechanism (almost background free with e.g SuperNEMO). Possibility to access Majorana CP phases. Scenario 2 2020 2012 2015 “Ton” detector construction Understanding backgrounds and limiting factors (Radon?) with O(100kg) experiments Isotope enrichment technology. “Background-free” detector technology and isotope(s) choice. “Ton” Experiment must have the sensitivity to establish or exclude the IH 31

  32. Summary • 0νββ is the onlyway to answer questions on Full Lepton Number violation and nature and mechanism behind neutrino mass • Reach interplay with other areas • Neutrino mass from end-point β-decay • Neutrinos in cosmology • Neutrino oscillations • Several next generation experiments starting in the next few years • K-K “claim” tested • Benchmark sensitivity of 50 meV • Need a common strategy based on results of the above to get down to 10 meV (and lower?). • We should get away from “setting limits mindset” and look for discovery!

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