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The CUORE EXPERIMENT: A search for neutrinoless double beta decay

The CUORE EXPERIMENT: A search for neutrinoless double beta decay. 2 nd International Conference on Particle Physics in Memoriam Engin Arık and Her Colleagues Istanbul, Turkey 20 - 25 June 2011. Marco Andrea Carrettoni on behalf of the CUORE collaboration. Outline.

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The CUORE EXPERIMENT: A search for neutrinoless double beta decay

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  1. The CUORE EXPERIMENT: A searchforneutrinolessdouble beta decay 2nd International Conference on Particle Physics in Memoriam EnginArık and Her Colleagues Istanbul, Turkey 20 - 25 June 2011 Marco Andrea Carrettoni on behalfof the CUORE collaboration

  2. Outline • Theoretical and experimentalcontext: • NeutrinolessDouble Beta Decay (0n-DBD) • Sensitivity • BolometricApproach • The CUORE experiment • Set-up and properties • CUORICINO: the demonstrator • On the road to CUORE: CUORE-0 • Conclusions

  3. WhyNeutrinolessDouble Beta Decay? Effective Majorana Mass Nuclearmatrixelement DBD rate Phasespace

  4. Probing the neutrino mass Strumia&Vissanihep-ph/0503243

  5. dN/dE Signature and sensitivity In a source=detectorapproachweexpect a peak at the q-value Q of the transition (energy sum of the twoelectrons) Q Electrons energy Sensitivity: Defined as the decay time corresponding to the minimum number of detectable events above a background (B) at a given C.L.

  6. Bolometricapproach 6 • IdealCalorimeter: Energy tophononsconversion Thermalbath (copper) @ 10mK Weakthermalcoupling (Teflon) NTD Ge thermistor R100 MW TeO2 Crystal Absorber C  10-9 J/K • Pros: • Highresolutions • Wide choiceofmaterials • Cons: • Slow signals • No particledistinction • Operatingprinciple: • Dielectric and diamagneticcrystals: low thermalcapacity @ low temperature

  7. Energy absorber & temperature sensor TeO2cubiccrystal NTD-Gethermistor • 5x5x5 cm3 • - The choice of the material isdrivenby the choice of the candidate nuclide • 3x3x1 mm3 • - Ge dopedbyNeutronTransmutation Doping TeO2 130Te 1. ~2527 keV A. Dielectricwith TD=232 K: C minimized B.Easy togrowlargecrystalswithgoodradio-purity C. Resistancetoseries of thermalcycles at very low temperatures 2. A typicalacquiredparticlesignal

  8. CUORE (Cryogenic Underground Experimentfor Rare Events) Pulse Tube (L He-freecryostat) • 988 TeO2crystals 5x5x5cm3 (750g), arranged in 19 towers; • 741 kg of TeO2 -> 206 kg of130Te • Resolution 5 keV @ 2615 keV (FWHM) • Background aim: 0.01-0.001 c/keV/kg/y • Mainconcepts: • Stringentcontrols on radioactivity • Heavyshielded (Roman lead) • High efficiency in bkgrejectionthankstoclosepacketgeometry Polyethilene (NeutronsShieldings) CopperShielding ExternalLead Shieldings (210 Po<14 mBq/kg) Roman LeadShieldings (210 Po<4 mBq/kg) Detector

  9. LNGS CUOREwillbelocated in the Hall A of the Gran Sassonationallaboratories (L’Aquila – Italy) • Depth: 3650 m.w.e. • Muonflux: (2.58±0.3)x10-8m/s/cm2 • Neutronflux 4x10-6 n/s/cm2 • Gamma flux: 0.73 g/s/cm2 • Cosmicrays are not a problem!

  10. The CUORE program CUORICINO 2003-2008 CUORE – 0 2011 - 2014 CUORE 2014-2019 19 Tower 998 crystals M 206 kg of130Te Bkg 0.01 ÷ 0.001 c/keV/kg/yr 1 Tower 62 crystals M 11 kg of130Te Bkg  0.15 c/keV/kg/yr 1 Tower 52 crystals M11 kg of130Te Bkg 0.05 ÷ 0.1 c/keV/kg/yr

  11. Cuoricino: the demonstrator The bolometrictechniquehasbeenappliedto the search of the following 0v-DBD: 130Te 130Xe + 2e- Q0v~2527 keV The Cuoricino experiment (LNGS, 2003-2008) is the result of years of research on bolometerscontaining130Te, byusing TeO2 energyabsorbers • Cryostat • LeadShield (20 cm) • Neutronshieldofborated • Polyethilene • Roman LeadShield • (210Po < 4mBq/kg) Mass 40.7 kg TeO2 (11.3 kg 130Te) Total exposure 19.75 kg y [130Te]] y

  12. Cuoricino mainoperatingprinciple • The analysisiscarried out on anti-coicinidencespectra in orderto reduce: • Contributionfromcrystalsurfaces • Compton or multi-comptonevents • Accidentalcoincidences 0.7% • Bkgreduction : 15% TeO2 TeO2 Single Hit EventsDouble Hit Events TeO2

  13. 0n-DBD regionof interest • The anti-coincidencespectrum in the regionof interest showsthreemainpeaks: • 208Tl : (probably in the cryostat) • 60Co: cosmogenicorigin • 214Bi: Rncontamination • The main background contributions are: • Multicomptoneventsof208Tl (30%) • Flat background comingfromdegradedalphas on the surfaceofmaterialsfacing the crystals • (70%) R.O.I. 214Bi 208Tl 60Co (g+g) Flat continuum 0nDBD Normalizedcalibration escaped Te X-ray

  14. Cuoricino ResultAstropart. Phys. (2011), doi:10.1016/j.astropartphys.2011.02.002 Method: • Best fit: maximumlikelihood-chisquare • Limit: bayesian (flatprior on G0n) Avg Background in the regionof interest: 0.169±0.006 c/keV/kg/y Avgresolutio: ∆E7 keV FWHM mee<300-701meV* t0nbb1/2 > 2.8x1024 y @ 90% CL UUnphysical region • * Spread introducedby NME 60Co

  15. Twoparallelanalysis: validation on Monte Carlo • Twoindepententanalysiswerecarried out on data and simulationwithanexeptional agreement • Both the methodsprovedtobeunbiased and robust. • On the simulations (1000 Cuoricino-likeexperiments) they show a wide distributionofpossibleoutcomes. • The medianoutcomeoftheseexperimentscorrespondsto a limit on the half life of 2.6x1024 y comparableto the experimentallimit

  16. From Cuoricino to CUORE • Extensivestudyof the background sources • Design of the experiment • Cryostat and shieldings • Radioactivitycontrol • Electronics • DAQ • Crystals • Software • Calibration system • Towerassembly • … Challengingeffort on everycrucialaspectsof the experiments

  17. CUORE Crystals The 1000 CUORE crystals are producedby SICCAS (Shanghai, China): - 560 crystalsorderedby INFN (now@LNGS); - 500 crystalorderedbyDoE (91 already in @LNGS, end in Sept. 2012) Foreach production batch 2 or more crystals are tested in the Hall C R&DCryostat: - Same single moduleas CUORE; - New Data Acquisition and online as CUORE; - All material cleanedCUORE-like; 6 CCVR measurementswereanalyzed (preliminaryresults): Surface : < nBq/cm2 Resolution : avg ∆E = (4.9 ± 1.9) keV FWHM preliminary < 6 · 10−14 g/g in 238U < 8 · 10−14 g/g in 232Th Bulk: Production requirements perfectlyfulfilled!

  18. The answerto CUORE-0 The full assembly of a CUORE-like tower: data taking starts this fall High statistic test of the background achievements: crucial importance for surface background studies Two irreducible background predicted (realistic and optimistic case) CUORE-0 will be a competitive 0nDBD experiment itself!

  19. CUORE scientific goal In 5 years of live time, CUORE has a 1σ sensitivity of tDBD1/2 = 2.1x1026 y ⇒ effective Majorana neutrino mass down to 35 ÷ 82 meV With the foreseen aim of 0.01 c/keV/kg/y CUORE will be able to probe the inverted scale

  20. Conclusions • Te02 bolometersprovedtobe a competitive toolfor the DBD search • Cuoricino provedtobenotonlyanimportantexperiment, butalso a greatprototype, showingthatanexperimentlike CUORE isfeasible • CUORE-0 willbe the first test of a CUORE-liketowerfrom the assemblyto data taking and a competitive experimentitself • CUORE data takingisforeseenfor 2014

  21. Conclusions Thankyouforyouattention

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