First neutrinoless double beta decay results from CUORE-0 Università degli Studi di Milano - Bicocca INFN di Milano - Bicocca First neutrinoless double beta decay results from CUORE-0 L. Gironi on behalf of the CUORE collaboration 10th  M E D E X '15  meeting Prague, June 09th - 12th, 2015 

Bolometers for 0νDBD Why bolometers are suitable detectors for 0νDBD ? Parameters Bolometers Maximum sensitivity achievable regardless of Δ and B (zero background limit) - Possibility to choose among all the ββ isotope - optimization of a - Very high detection efficiency (ε) (source=detector) ∆ Fundamental in 0νDBD studies because of the 2νDBD - Excellent energy resolution (~5 keV at Q-value) B In many cases it is still possible to act on it to greatly improve the sensitivity - Q-value in low background region - Very low background level already reached but surface contaminations

Energy release → ΔT→ ΔR in the thermistor → ΔV TeO2 Bolometric Detectors At 10 mK, energy deposited in TeO2 results in a measurable change in temperature Energy release → ΔT→ ΔR in the thermistor → ΔV ΔTtherm~ 10-20 μK/MeV ΔTcryst ~ 0.1 mK/MeV ΔRtherm ~ 3 MΩ/MeV ΔVtherm ~ 0.3 mV/MeV 130Te is one of the best candidates for 0νDBD search: • favorable Q-value (2528 keV) • highest isotopic abundance (~34%), no enrichment for present generation experiments • large mass, high purity, highly reproducible detectors can be built with TeO2

The CUORE program Search for 0νDBD of 130Te with TeO2 bolometers M: Scale up mass (~20x) T: Cryogen-free dilution refrigerator ∆: Improve energy resolution B: Reduce background (~20x) Cuoricino 2003-2008 M· T (130Te) = 19.75 kg.yr B = 0.169 ± 0.006 c/keV/kg/y ∆ = 6.3 ± 2.5 keV FWHM T1/2 > 2.8· 1024 y (90% C.L.) CUORE 2015-2020 M· T (130Te) = 1030 kg.yr B = 0.01 c/keV/kg/y ∆ = 5 keV FWHM T1/2 = 9.5· 1025 y (90% C.L.)

Cuoricino T1/2 > 2.8 x 1024 y (90% C.L.) 62 TeO2 crystals (40.7 kg) operated at Gran Sasso (2003-2008) T1/2 > 2.8 x 1024 y (90% C.L.) • M· T (130Te): 19.75 kg.yr • ∆: 6.3 ± 2.5 keV FWHM • B: 0.169 ± 0.006 c/keV/kg/yr 0νββ upper limit mββ < (270-650) meV (R)QRPA - Phys.Rev. C 77 045503 (2008) pnQRPA - JoP Conference series 173 012012 (2009) ISM - Nucl. Phys. A 818 139 (2009) IBM-2 - Phys.Rev. C 79 044301 (2009)

Main sources of background in the ROI: Cuoricino – Background β/γ events α events Qββ Physics data Calibration data Main sources of background in the ROI: Qββ 30% Compton from 208Tl decays in cryostat 60% Degraded alphas on copper surfaces 10% Degraded alphas on crystal surfaces α

CUORE-0 is the first tower produced out of the CUORE assembly line. 52 TeO2 5x5x5 cm3 crystals (~750 g each) 13 floors of 4 crystals each Total detector mass: 39 kg TeO2 (10.9 kg of 130Te) Purpose: Commission assembly line Minimization of Rn exposure (Glove Box assembly) Validate CUORE detector design New (lighter) detector design structure New surface cleaning technique (TECM) Provide test bed for developing DAQ & analysis framework Run as standalone experiment while CUORE is being constructed

Clean Room for Detector Assembly and Storage CUORE/CUORE-0 – Assembly line Clean Room for Detector Assembly and Storage CUORE hut Cuoricino/ CUORE-0 hut CUORE-0 construction was carried out inside N2-flushed glove boxes in CUORE hut’s clean room.

CUORE/CUORE-0 – Assembly line Semi-automatic gluing line • Attach NTD, heater to each crystal • Completely enclosed in N2 fluxed glove box • Minimizes human interaction with parts • Automatic, highly reproducible glue deposition

CUORE/CUORE-0 – Assembly line Tower contruction • Unpack ultra-cleaned copper/PTFE parts and quality- check in N2 atmosphere • Parts and crystals for a floor transferred under vacuum to assembly glove box • Build up tower floor-by-floor in N2 atmosphere, completed floors lowered into N2-fluxed ‘garage’ • Readout wire-strips glued to arms and attached to tower in N2 flushed glove box

CUORE/CUORE-0 – Assembly line Connection to readout: Wire bonding • All wire-bonding done in N2 flushed glove box • Vertical bonding machine with auxiliary X-Y motion

and of the CUORE cleaning procedures. CUORE/CUORE-0 – Assembly line Tower storage CUORE-0 with 10mK shield CUORE tower The successful operation of CUORE-0 demonstrated the validity of the CUORE tower assembly line and of the CUORE cleaning procedures.

CUORE-0 • Uses the old Cuoricino cryostat • Electronics from Cuoricino • Shielding from Cuoricino • Cooled to base T (~10 mK) Mar 2013

CUORE-0 – Data taking M· T (130Te): 9.8 kg· yr of 130Te 51/52 NTDs online 50/52 heaters online Calibration data taking Physics data taking 1st campaign 2nd campaign

The 5 keV CUORE goal has been reached CUORE-0 – Calibration energy resolution Total fit on the 2615 keV line Distribution of energy resolution @ 2615 keV CUORE-0 Preliminary CUORE-0 Preliminary Exposure-weighted Harmonic Mean FWHM RMS of FWHM Cuoricino 5.8 keV 2.1 keV CUORE-0 4.9 keV 2.9 keV The 5 keV CUORE goal has been reached

Comparison of the total background spectrum in CUORE-0 and Cuoricino CUORE-0 – Background Comparison of the total background spectrum in CUORE-0 and Cuoricino CUORE-0 Preliminary 2.7-3.9 MeV [c/keV/kg/y] eff [%] Cuoricino 0.110 ± 0.001 83 ± 1 CUORE-0 0.016 ± 0.001 81 ± 1 a factor ~7 reduction in the alpha continuum region ɣs from U chain reduced with radon control residual ɣ bkg in ROI from Th cryostat contaminations (negligible in CUORE)

CUORE-0 – 0νDBD analysis Total selection efficiency = (81.3 ± 0.6)% Data processing and analysis techniques are focused to the correct reconstruction of each event energy (optimal filtering technique) and eventually to the creation of the energy spectrum of the ROI: Pile-up removal: multiple events in the same acquisition window are rejected Pulse shape discrimination: events with unexpected shape are rejected Anti-coincidence: only single crystals events are signal candidates efficiency [%] error Trigger 98.529 0.004 Pile-up and PSA 93.7 0.7 Event containment 88.4 0.09 Accidental coincidence 99.64 0.10 Total selection efficiency = (81.3 ± 0.6)%

0.058 ± 0.004(stat.) ± 0.002(syst.) c/keV/kg/y CUORE-0 – 0νDBD search After all cuts: 233 events in ROI [2470-2570 keV]. Best value fit of the 0νDBD decay rate: Г0ν= 0.01 ± 0.12(stat.) ± 0.01(syst.) x 10-24 yr-1 Background index in ROI: 0.058 ± 0.004(stat.) ± 0.002(syst.) c/keV/kg/y CUORE-0 Preliminary CUORE-0 Preliminary Profile negative log-likelihood We find no evidence for a signal and set 90% C.L. lower limit from profile likelihood:

CUORICINO/CUORE-0 combined limit We combine the CUORE-0 result with the existing 19.75 kg· yr of 130Te exposure from Cuoricino CUORE-0 Preliminary Profile negative log-likelihood This is the most stringent limit on this half-life !

Extrapolation to mββ mββ < (270-650) meV CUORE-0 Preliminary Combined half-life result as a limit on the effective Majorana neutrino mass: mββ < (270-650) meV IBM-2 Phys. Rev. C 91, 034304 (2015) QRPA-TU Phys. Rev. C 87, 045501 (2013) pnQRPA Phys. Rev. C 91, 024613 (2015) ISM Nucl. Phys. A 818, 139 (2009) EDF Phys. Rev. Lett. 105, 252503 (2010)

The CUORE program Search for 0νDBD of 130Te with TeO2 bolometers M: Scale up mass (~20x) T: Cryogen-free dilution refrigerator ∆: Improve energy resolution B: Reduce background (~20x) Cuoricino 2003-2008 M· T (130Te): 19.75 kg.yr B = 0.169 ± 0.006 c/keV/kg/y ∆ = 6.3 ± 2.5 keV FWHM T1/2 > 2.8· 1024 y (90% C.L.) CUORE 2015-2020 M· T (130Te): 1030 kg.yr B = 0.01 c/keV/kg/y ∆ = 5 keV FWHM T1/2 = 9.5· 1025 y (90% C.L.)

CUORE Goals: 988 TeO2 5x5x5 cm3 crystals (~750 g each) 19 towers identical to CUORE-0 (13 floors of 4 crystals each) total detector mass: 741 kg of TeO2 (206 kg of 130Te) • newly designed dilution refrigerator made of low radioactivity materials - Technologically challenging: ~1 ton of detectors at 10 mK - Independent suspension of the detector array from the dilution unit: smaller vibrational noise Goals: • build a 1-ton bolometric detector • energy resolution @ ROI: 5keV • background level: 0.01 c/keV/kg/y • sensitivity (90% C.L., 5 years):

CUORE – Background mitigation efforts Improve shielding and radio-purity of cryostat materials Neutron shield (18 cm PET + 2cm of H3BO3) External lead shield (thickness >35 cm) Low-radioactivity copper for cryostat vessels and flanges Internal lead shield (low-radioactivity/ancient lead) Improve radio-purity of active and inert surfaces in the detector Ultra-pure TeO2 crystals Cu frame optimized to reduce surface area facing the crystals New ultra-cleaning for all Cu components: - Tumbling - Electropolishing - Chemical etching - Magnetron plasma etching

CUORE – Self shielding CUORE-0: All bolometers face 10 mK shield CUORE: Only outermost crystals face 10 mK shield

CUORE – Status Assembly of the 19 CUORE towers is complete Expect to deploy the array in the cryostat later this year.

CUORE – Status Cryostat assembled, passed 4K commissioning test Dilution unit delivered to LNGS, able to maintain ~5mK in standalone commissioning tests Final integration run (everything except detectors) is ongoing Outermost shield Cryostat Vessel Flanges Diluition unit Plan to start operations by end of 2015.

? The CUORE program Cuoricino 2003-2008 M· T (130Te) = 19.75 kg.yr B = 0.169 ± 0.006 c/keV/kg/y ∆ = 6.3 ± 2.5 keV FWHM T1/2 > 2.8· 1024 y (90% C.L.) CUORE 2015-2020 M· T (130Te) = 1030 kg.yr B = 0.01 c/keV/kg/y ∆ = 5 keV FWHM T1/2 = 9.5· 1025 y (90% C.L.) CUPID … M· T· ∆· B ≈ 0

CUORE Upgrade with Particle ID (CUPID) Beyond CUORE Next generation bolometric experiment for 0νββ searches aims to use active rejection techniques to drastically reduce the background: CUORE Upgrade with Particle ID (CUPID) arXiv:1504.03599

Conclusions TeO2 bolometers offer a well-established, competitive technique in the search for 0νDBD CUORE-0 Achieved its energy resolution and background level goals. Indicated CUORE sensitivity goal is within reach. Did not find evidence of 130Te 0νDBD and after combination with CUORICINO data set the best limit to date on T1/2 of the decay. CUORE Assembly of the 19 CUORE towers is complete. Commissioning of the cryogenic system and experimental infrastructure is in progress. Plan to start operations by the end of 2015.

The CUORE Collaboration