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The CUORE experiment: a search for neutrinoless Double Beta Decay

This article discusses the search for neutrinoless double beta decay, an extremely rare process that can provide insights into neutrino mass and nature. It explores the experimental approach using the bolometric technique and focuses on the 130Te isotope as a candidate for this decay.

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The CUORE experiment: a search for neutrinoless Double Beta Decay

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  1. The CUORE experiment: a search for neutrinoless Double Beta Decay Luca Gironi on behalf of the CUORE collaboration NEW TRENDS IN HIGH-ENERGY PHYSICS Alushta, CrimeaSeptember 3-10, 2011

  2. Outline • Neutrino mass • Neutrinoless Double Beta Decay • Experimental approach • the bolometric technique • Cuoricino • the detector • the background • the 130Te half life limit • CUORE • the detector • status • scientific goal • Conclusion Alushta – 6 September 2011 Luca Gironi

  3. Neutrino oscillations and the neutrino mass • Neutrino oscillation experiments have convincingly established that neutrinos have mass • However, the absolute mass scale and the mass hierarchy are still not known If neutrino has a nonzero rest mass, mass eigenstates (ν1, ν2, ν3) and weak interactions eigenstates (νe, νμ, ντ) do not necessarily have to coincide • Great interest for non-oscillation experiments able to study absolute neutrino mass scale and its nature: • βdecay experiments • neutrinoless Double Beta Decay (0νDBD) experiments • cosmological observations Alushta – 6 September 2011 Luca Gironi

  4. The neutrino mass: cosmology, single and double beta decay Cosmology, single and 0νDBD measure different combinations of the neutrino mass eigenvalues, constraining the neutrino mass scale. In a standard three active neutrino scenario: incoherent sum real neutrino bdecay coherent sum virtual neutrino Majorana phases 0νDBD αi=Majorana phases simple sum pure kinematical effect cosmology Alushta – 6 September 2011 Luca Gironi

  5. Combine the informations mb [eV] S [eV] mbb [eV] The three mass scale parameters can be plot as a function of the lightest neutrino mass. Two bands appear in each plot, corresponding to inverted and direct hierarchy. The two bands merge in the degenerate case (the only one presently probed). • Strumia, F.Vissani • arXiv:hep-ph/0606054v3 Alushta – 6 September 2011 Luca Gironi

  6. Primary role of neutrinoless Double Beta Decay 2νDBD 0νDBD • Neutrinoless Double Beta Decay (0νDBD): • Requires neutrino is a massive particle • Violates lepton number (ΔL=2), implies physics beyond Standard Model • Allows to investigate neutrino nature: Dirac or Majorana Alushta – 6 September 2011 Luca Gironi

  7. 0νDBD and neutrino mass • Extremely rare process (T0ν1/2 > 1024 y): 0νDBD never observed (except a discussed claim in 76Ge) • T0ν1/2is the 0νββ half-life • G0ν(Q,Z) is the 'accurately calculable' phase space factor proportional to (Q-value)5 • M0ν is the Nuclear Matrix Element (NME), which carries a theoretical uncertainty of a factor of ~2-3 depending on the nucleus • <mββ> is effective double-beta neutrino mass • Possible for ~35 nuclei, only ~10 really interesting Alushta – 6 September 2011 Luca Gironi

  8. 0νDBD: experimental approach ββsummed e− energy spectrum • Signature: Two simultaneous electrons with summed energy Qββ, the Q-value for ββ in the isotope under study • Experimentalists measure the decay rate looking at a peak in the energy spectrum 2νββ 0νββ • Detector Sensitivity (S): the process half-life corresponding to the maximum signal that could be detected T : measurement live time [y] M : detector mass [kg] B : background [c/keV/kg/y] Δ: energyresolution [keV] η: stoichiometric coefficient W: molecular weight of the active mass a: isotopic abundance (i.a.) ε: detector efficiency Alushta – 6 September 2011 Luca Gironi

  9. Experimental approaches To reach a high sensitivity: high efficiency (source = detector) high i.a. or enrichment possibility large detector mass (100-1000kg ) very low-background (underground, shieldings, ...) excellent energy resolution Some of the under construction/funded experiments: Other experiment: CANDLES, Majorana, COBRA, MOON, ... J.J. Gómez-Cadenas et al JCAP06(2011)007 Alushta – 6 September 2011 Luca Gironi

  10. Experimental approaches: the bolometric technique • Among the different techniques excellent results can be obtained if source=detector • The bolometric technique offers several advantages: • Excellent energy resolution • Large source mass • High efficiency • Possibility to study all the 0νDBD isotope (cross checks) Bolometric technique: the working principle Crystals, cooled to ~10 mK inside a dilution-refrigerator cryostat, have such small heat capacities that single particle interactions produce measurable rises in temperature. C = heat capacity G = thermal conductance Alushta – 6 September 2011 Luca Gironi

  11. 130Te as 0νDBD candidate • 130Te • High natural abundance (i.a. 130Te ~ 34%): no need for enrichment • Q-value at ~2528 keV is above the energy range of most naturally occurring γ rays • TeO2 crystals • favorable characteristics of these crystals if compared with Te: • higher Debye temperature • rather good mechanical properties and it is possible to grow large crystals • good intrinsic radiopurity (< 1 pg/g in 232Th and 238U) Alushta – 6 September 2011 Luca Gironi

  12. Evolution of the bolometric technique All are cryogenic bolometer experiments searching for 0νDBD decay in 130Te Cuoricino CUORE-0 CUORE Cryogenic Undergound Observatory for Rare Events 2011 - 2014 2003 - 2008 2014 - 2019 11 kg 130Te 206 kg 130Te 11 kg 130Te Alushta – 6 September 2011 Luca Gironi

  13. LNGS underground facility CUORE hut Laboratori Nazionali del Gran Sasso (LNGS), Italy • Underground facility • Average depth ~ 3650 m.w.e. • Factor 106 reduction in muon flux to ~ 3×10—8μ/(s·cm2) NE Alushta – 6 September 2011 Luca Gironi Cuoricino/ CUORE-0 hut

  14. Cuoricino experiment • CUORE predecessor • Operated March 2003 - May 2008 • 62 TeO2 crystal bolometers: • 44 crystals 5x5x5 cm3, (790 g) • 18 crystals 3x3x6 cm3 (330 g) • 14 “natural” crystals • 2 enriched in 130Te (75%) • 2 enriched in 128Te (82%) • 40.7 kg TeO2 11.3 kg 130Te Alushta – 6 September 2011 Luca Gironi

  15. Cuoricino energy spectrum Cuoricino single-hit background spectrum (black) and normalized 232Th calibration spectrum (red) Degraded alpha energy tail Gamma domain Alpha domain • Anticoincidence cuts • 0νDBD decay should produce a single-site signal 85% of the time • Excluding multi-site events reduces background by ~ 15% in the region of interest • Surface α contamination • the main source of flat background in 3-4 MeV region due to degraded α particles Alushta – 6 September 2011 Luca Gironi

  16. Cuoricino backgrounds 208Tl 214Bi 60Co −Cuoricino single-hit background spectrum −232Th calibration spectrum (normalized) • There are three main sources of background in the region of interest: • ~40% multi-Compton events from 2615 keV γ peak of 208Tl • ~ 50% degraded alphas from 238U and 232Th on copper surfaces • ~ 10% degraded alphas from 238U and 232Th on crystal surfaces Alushta – 6 September 2011 Luca Gironi

  17. Cuoricino results 130Te 0νDBD Total statistics 19.75 kg·yr 130Te exposure Average energy resolution (FWHM): Background: 130Te half-life limit: Effective neutrino mass limit: 6.3±2.5 keV at Q-value in big crystals 0.169 ± 0.006 counts/keV/kg/y > 2.8 × 1024 y (90% C.L.) mββ < 300-710 meV uncertainty due to N.M.E. Alushta – 6 September 2011 Luca Gironi

  18. CUORE-0 • Single CUORE-like tower • (52 Te02 crystals chosen from CUORE crystals) • test of CUORE assembly and cleaning procedures • deliver information about backgrounds • sensitive 0νDBD experiment • same assembly procedures as CUORE • same cleaning procedure as CUORE • very similar copper frames and Teflon holder • Operated in refurbished Cuoricino cryostat • different suspension than CUORE • different shielding • CUORE-0 tower construction will start Oct. 2011 • Data taking starts within 2011 Alushta – 6 September 2011 Luca Gironi

  19. CUORE Closely packed array of 988 TeO2 crystals (5x5x5 cm3 750 g) - 19 towers • -13 planes each • - 4 crystals each CUORE detector improvements • Cleaner crystals • Higher granularity (reduction alpha background due to crystal surface thanks to anticoincidence) • Cleaner copper and less per kg TeO2 • Cleaner assembly environment • Copper frames less vibration-sensitive • Better self-shielding 741 kg TeO2 granular calorimeter 206 kg of 130Te Alushta – 6 September 2011 Luca Gironi

  20. CUORE CUORE cryostat improvements • Cryogen-free: better duty cycle • Detector suspension independent of refrigerator apparatus • Stringent radiopurity controls on materials and assembly CUORE shieldings improvements • Minimum lead thickess ≈ 36 cm (in Cuoricino ≈22 cm) • 6 cm thick lead shield operated at ~10 mK surround the array • 30 cm of low activity lead will be used to shield from the dilution unit and from the environmental radioactivity • Neutron shielding: 18 cm thick polyethylene + 2 cm of H3BO3 powder Alushta – 6 September 2011 Luca Gironi

  21. CUORE CUORE crystals • The production started at SICCAS Jiading in 2008 • ~ 30 crystals/month • ~ 700 crystals already at LNGS • CUORE Crystal Validation Run – CCVR: a dedicated cryogenic setup to test crystals randomly chosen • 7 CCVR already performed: • the bulk activity is within the limit specified in the contract with the crystals producer • improved the Cuoricino bolometric performance • FWHM on the internal alphas from 210Po (5407 keV) = 5.2 keV on average • lowered the energy thresholds thanks to a new trigger algorithm • - a better understanding of the background • - possibility to study Dark Matter spin independent interaction with CUORE Alushta – 6 September 2011 Luca Gironi

  22. CUORE schedule 2008: Hut construction Crystal production 2009–2010: Crystal production Engineering/design/fabrication 2011: Crystal production Clean room commissioning CUORE-0 2012–2013: CUORE detector assembly CUORE cryogenics CUORE electronics & DAQ 2014: Data taking! CUORE hut Crystal handling robot Gluing tests Tower garage Bonding tests Alushta – 6 September 2011 Luca Gironi

  23. CUORE scientific goal In 5 years of live time, with the foreseen aim of 0.01 c/keV/kg/y CUORE has a 1σ sensitivity of Alushta – 6 September 2011 Luca Gironi

  24. Conclusions • 0νDBD plays a primary role in the study of neutrino nature, in the study absolute neutrino mass scale and has a special relevance for testing the physics beyond the standard model • Te02 bolometers proved to be a competitive tool for the DBD search • Cuoricino has provided the most stringent limits on 0νDBD of 130Te and showed that an experiment like CUORE is feasible • CUORE-0 will be the first test of a CUORE-like tower from the assembly to data taking and a competitive experiment itself • CUORE data taking is foreseen for 2014 Alushta – 6 September 2011 Luca Gironi

  25. Conclusions Thank you for the attention! Alushta – 6 September 2011 Luca Gironi

  26. Fine

  27. Backup slides

  28. Nuclear Matrix Elements 130Te half-life limit (90% C.L.): T0ν1/2>2.8 x 1024 y Effective neutrino mass limit: mββ < 300÷710 meV NME bibliography: J. Barea et al., Phys. Rev. C 79, 044301 (2009) F. Simkovic et al., Phys. Rev. C 77, 045503 (2008) O. Civitarese et al., J. Phys. Conf. Ser. 173, 012012 (2009) J. Menendez et al., Nucl. Phys. A 818, 139 (2009) Alushta – 6 September 2011 Luca Gironi

  29. 0νDBD experiments: comparison Sense and sensitivity of double beta decay experiments J.J. Gomez-Cadenas et al. Journal of Cosmology and Astroparticle Physics June 2011 Alushta – 6 September 2011 Luca Gironi

  30. 0νDBD experiments: comparison Sense and sensitivity of double beta decay experiments J.J. Gomez-Cadenas et al. Journal of Cosmology and Astroparticle Physics June 2011 Alushta – 6 September 2011 Luca Gironi

  31. CUORE: Dark Matter Alushta – 6 September 2011 Luca Gironi

  32. CUORICINO coincidence analysis __ single hit events __ double hit events 238U and 232Th alpha peaks due to crystal surface contaminations Alushta – 6 September 2011 Luca Gironi

  33. CUORE: the hut 2nd - electronics 1st - clean room 0th – cryostat equipment Alushta – 6 September 2011 Luca Gironi

  34. CUORE gluing station, garage and working plane Crystal handling robot Epoxy mixing/dispensing robot Universal Working Plane Tower garage Bonding tests Alushta – 6 September 2011 Luca Gironi

  35. CUORE status: the cryostat • 4 companies to pour, work, and form low-rad copper into 6 vessels (+ flanges) • First 3 vessels (300K, 40K, 4K) are in process of being electron-beam welded • Delivery scheduled for Sep 2011 • More delicate inner 3 vessels will be manufactured next year Alushta – 6 September 2011 Luca Gironi

  36. Cuoricino cosmic background study 1.1 μ/hr/m2 • 10 plastic scintillators were arranged around cryostat during final 3 months of Cuoricino data taking • Searched for correlations between muon triggers and single-site events in bolometer array • Measured rate was consistent with zero in the 0νββ region of interest (R.O.I.), corresponding to an upper limit of: • Cuoricino background in R.O.I. is much higher: Rμ < 0.0021 counts/keV/kg/y (95% C.L.) E. Andreotti et al. (CUORICINO Collaboration), Astropart.Phys.34:18-24 (2010) [arXiv:nucl-ex/0912.3779]. RCuoricino ~ 0.2 counts/keV/kg/y Alushta – 6 September 2011 Luca Gironi

  37. Pulse shape and anticoincidence cuts Alushta – 6 September 2011 Luca Gironi

  38. Cuoricino analysis sequence • Pulse amplitude evaluation • Pulse amplitude is the paramount observable, because it’s proportional to the amount of energy deposited • Raw pulse is processed using so-called Optimum Filter (OF) • Gain stabilization • Bolometer gain is temperature-dependent, so... • Detector response varies with natural temperature drift • Gain is “stabilized” by plotting heater pulse amplitude vs. baseline and fitting a line to the points • Energy calibration • Need to convert the stabilized pulse amplitudes to energy • Thorium sources were lowered next to detector ~ once/month • Global and pulse shape cuts • Used to reject nonphysical events (e.g., electronic noise) and pileup events • Anticoincidence cuts • 0νββ decay should produce a “single- site” signal 85% of the time • Excluding multi-site events (±50 ms) reduces background by ~ 15% in the region of interest while retaining more than 99% of signal • Energy spectrum fit Alushta – 6 September 2011 Luca Gironi

  39. What is the most favorable isotope and the best technique ? • Phase space factor: 48Ca, 150Nd, 96Zr • Nuclear matrix element  not yet reliable predictions • Backgrounds > 2,6 MeV 48Ca, 150Nd, 96Zr, 100Mo, 82Se, 116Cd • > 3.2 MeV (radon) 48Ca, 150Nd, 96Zr • Enrichment:130Te (Natural isotopic abundance 34%) • 136Xe (gaz, easy to enrich) • Best techniques : • Bolometers, Ge diodes: energy resolution 130Te (82Se, 116Cd), 76Ge • Tracko-calo : background rejection82Se, (48Ca, 150Nd) • TPC Xe: background rejection if tagging of Ba 136Xe • Large liquid scintillator: mass of isotopes 136Xe, 150Nd Alushta – 6 September 2011 Luca Gironi

  40. Ge diode detectors Heidelberg-Moscow (2001) ~11 kg of enriched 76Ge (86%) IGEX (2002) ~ 8.4 kg of enriched 76Ge (86%) 8.9 kg.yr without PSA 4.6 kg.y with PSA 0.06 cts/keV/kg/yr T 1/2 >1.9 1025 yr (90% CL) T 1/2 >1.57 1025 yr (90% CL) <mn> <0.35-1.05 eV (90% CL) <mn> <0.33-1.31 eV (90% CL) Eur. Phys. J., A 12 (2001) 147 Phys. Rev. D65 (2002) 092007 Alushta – 6 September 2011 Luca Gironi

  41. NEMO3 E1+E2= 2088 keV t= 0.22 ns (vertex) = 2.1 mm 82Se (0,93 kg) Tracko-calo detector Drift chamber (6000 cells) Plastic scintillator + PMT (2000) 10 kg of isotopes DE/E (FWHM) : 8 % @ 3 MeV Located in Modane Underground Lab (France) Bckg: 0.025 cts/keV/kg/yr Multi-source detector bb events E1 e- Vertex e- E2 Alushta – 6 September 2011 Luca Gironi

  42. SuperNEMO 1 m 5 m 20 modules for 100 kg Source (40 mg/cm2) 12m2 Tracking (~2-3000 Geiger cells). Calorimeter (500 channels) Total:~ 40 000 – 60 000 geiger cells channels ~ 10 000 PMT Top view Alushta – 6 September 2011 Luca Gironi

  43. SuperNEMO DE/E < 4% (FWHM) @ Qbb demonstrated (< 8% @ 1 MeV) Commissioning of wiring robot FWHM = 7,1 % (7,6% before energy loss correction) SuperNEMO phase I : 2011 – 2014 Contruction demontrator module with 7 kg of 82Se Commissing @LSM 2013 Sensitivity in 1 year: T1/2 < 5 1024 y <mn> < 0.2 – 0.6 eV SuperNEMO phase II : 2014 – 2019 100 kg of 82Se (or 150Nd,or 48Ca) T1/2 > 1026 y <mn> < 0.05 – 0.14 eV SuperNEMO @ LSM extension Alushta – 6 September 2011 Luca Gironi

  44. GERDA Removal of matter Use of liquid nitrogen or argon for active shielding Segmented detectors in futur Improvement of Pulse Shape Analysis PHASE I:17.9 kg of enriched 76Ge (from HM and IGEX) In 1 year of data if B=10-2 cts/keV/kg/yr (check of Klapdor’s claim) Start 2011 at Gran Sasso T1/2 > 3 1025 yr <mn> < 0.25 eV> PHASE II:40 kg of enriched 76Ge (20 kg segmented) 2012 if B=10-3 cts/keV/kg/an T1/2 > 2 1026 yr in 3 years of data <mn> <0.1 eV> Alushta – 6 September 2011 Luca Gironi

  45. GERDA • Nov/Dec.’09: Liquid argon fill • Jan ’10: Commissioning of cryogenic system • Apr/Mai ’10: emergency drainage tests of water tank • Apr/Mai ’10: Installation c-lock • May ’10: 1st deployment of FE&detector mock-up • June ‘10: Commissioning with natGe detector string • Soon: ……. Alushta – 6 September 2011 Luca Gironi

  46. Majorana Ge diodes Very pure material (Electroformed copper) Segmentation PSD improvement R&D phase 30-60 kg of 86% enriched 76Ge crystals Some of the crystals segmented • Bckg goal ~ 1 count/ROI/t-yr (after analysis cuts) • 30 kg of enriched Ge, running 3 yr. Data taking scheduled for 2011 T1/2 > 1. 1026 yr <mn> < 0.14 eV (could confirm or refute Klapdor’s claim) Collaboration with Gerda for 1 ton detector Alushta – 6 September 2011 Luca Gironi

  47. EXO-200 Liquid Xe TPC Ionization + scintillation DE/E (FWHM)= 3.3 % @Qbb Possibility of Baryum ion tagging by Laser florescence (136Xe  136Ba++ + 2 e 200 kg of 136Xe, no Ba ion tagging Installation in WIPP underground lab Possibility to measure bb(2n) EXO-200 full of natural Xe - Tuning on all systems - Engineering runs - Physics mode as soon as possible Alushta – 6 September 2011 Luca Gironi

  48. EXO-200 http://arxiv.org/abs/1108.4193v1 Alushta – 6 September 2011 Luca Gironi

  49. SNO++ Scintillator loaded with Nd 500 kg of 150Nd 1 year <mn> = 150 meV Test of light attenuation Study of Nd purification (factor 1000 per pass in Th and Ra) 56 kg of 150Nd (0,1 % of natural Nd) 4 yr of data <mn> ~0.08 eV 500 kg of 150Nd 4yr <mn> ~ 0.03 eV Alushta – 6 September 2011 Luca Gironi

  50. KamLAND-Zen Alushta – 6 September 2011 Luca Gironi

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