CUORE I.Nutini, GSSI - INFN LNGS; 103° Congresso SIF, 15 Set. 2017 Performance of the CUORE bolometers - First CUORE results - I.Nutini Gran Sasso Science Institute INFN Laboratori Nazionali del Gran Sasso on behalf of the CUORE collaboration 103° Congresso Nazionale della Società Italiana di Fisica Trento - Povo, 11-15 settembre 2017 1
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Performance of the CUORE bolometers · CUORE I.Nutini, GSSI - INFN LNGS; 103° Congresso SIF, 15 Set. 2017 Performance of the CUORE bolometers - First CUORE results - I.Nutini Gran
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(η = 33.8%) • 130Te within the detector absorber of TeO2
(high detection efficiency ε) • Reproducible growth of large number of
high quality crystals (M)
S
0⌫(n�) = ln2 ✏
1
n�
x ⌘ NA
MA
rM T
B �
Experimental 0vββ detection sensitivity:
- Lepton number violation process (BSM) - Majorana nature of neutrino - Constraints on neutrino mass hierarchy and scale - Not yet observed T0v > 1024-25 yr
• Closely packed array of 988 TeO2 crystals (19 towers of 52 crystals 5×5×5 cm3, 0.75 kg each) High Mass of TeO2: 742 kg (206 kg of 130Te ) and high granularity
• Low background: - Deep underground location (Gran Sasso National Labs - LNGS), - Strict radio-purity controls on materials
and assembly, - Passive shields (Pb) from external and cryostat radioactivity Background aim: 10-2 c/(keV⋅kg⋅yr)
• Low vibrations - Multistage cryogen-free cryostat: - Mass to be cooled down: ~15 tonnes (Pb, Cu and TeO2) - TeO2 detectors operating temperature: ~10 mK Energy resolution aim: 5 keV FWHM in the Region Of Interest (ROI)
CUORE S0v sensitivity in 5 years (90% C.L.): ~ 9 x 1025 yr
CUORE cooldown and data-takingCryogenic infrastructure and auxiliary systems
Detector Calibration System12 232Th γ-ray sources (thoriated tungsten) are cooled to base temperature and lowered into the experimental volume for calibration
Shieldings- External lead shielding and concrete support structure - Internal Ancient Roman Lead Shield (6 cm thick, 5 tons) @ 4K - Internal Top Lead Shield (30 cm thick, 2.5 tons) @ 50 mK
Multistage cryogen-free cryostat: - Fast Cooling System- 5 Pulse Tube cryocoolers (down to 4 K) - Continuous-cycle 3He/4He dilution refrigerator (down to base temperature ~10 mK)
- Cryogenic system commissioning : completed in Feb.2016 - Detector assembly and installation: completed at the end of Aug. 2016 - Detector cooldown: Started at the beginning of Dec. 2016, Cooldown time: ~ 20 days down to ~3.4 K, vacuum pumping into the inner volume, ~ 1.5 days down to ~ 10 mK
Observed first detector pulses just after the cool down without any optimization
Temperature scan: Temperature scan around base temperature to choose the one that optimizes the signal and at the same time allows to work with the designed NTD resistance. Selected working temperature: 15 mK
Setting the working points: Load curves scan to choose the best bias voltage to feed each channel’s NTD: • linear behavior for small temperature variations • maximization of signal to noise ratio • optimization of pulse amplitude
Detector characterization and first physics results0νββ analysis
Energy [keV]2400 2450 2500 2550 2600 2650 2700
Eve
nts [
coun
ts / k
eV]
02468
1012141618 Blinded
UnblindedTl208
Bi214 Co60
CUORE Preliminaryyr⋅Exposure: 38.1 kg
Fit to evaluate best fit decay rate for 130Te: Simultaneous unbinned extended maximum likelihood fit - ROI region: [2465,2575 keV] around Qββ (130Te). - Events selection efficiency: (62.6 ± 3.4)% - ROI background index:
(9.8–1.5+1.7) × 10-3 c/(keV⋅kg⋅yr)
Considering the overall 0νββ signal efficiency: (55.3 ± 3.0)% - Best fit decay rate: (-0.03–0.04+0.07(stat.) ± 0.01 (syst.)) × 10-24/yr
Half-life limit (90%C.L including syst.): T0ν (130Te) > 4.5 x 1024 yr
CUORE is the first tonne-scale bolometric 0νββ detector. First months of CUORE operations: • First CUORE physics results of T0ν in 130Te after 3 weeks of data taking • Exceptional cryostat performance and important information on
detectors characterization, noise, resolutions and background levels. • Detector optimization campaign focused on improving the resolution
through further noise reduction • Data taking has restarted at the end of July 2017, physics runs
Double beta decay is a very rare nuclear decay (N,Z) → (N-2, Z+2)
2vββ: - 2nd order process allowed in SM - Observed in several nuclei: !~1019-21 y 0vββ: - Lepton number violation process (BSM) - Majorana nature of neutrino - Constraints on neutrino mass hierarchy and scale - Not yet observed !>1024-25 y 2vββ
0vββ 1
T 0⌫1/2
/ G(Q�� , Z)|Mnucl|2|m�� |2
Phase space integral Nuclear matrix elementEffective neutrino mass termm�� = |⌃im⌫iU
CUORE cooldown and data-takingCryogenic infrastructure and auxiliary systemsMultistage cryogen-free cryostat: - Fast Cooling System- 5 Pulse Tube cryocoolers (down to 4 K) - Continuous-cycle 3He/4He dilution refrigerator (down to base temperature ~10 mK)
Detector characterization and first physics resultsDataset 2: Background spectrum
Background - Physics: Significant reduction in the γ region with respect to CUORE-0 (CUORE-like tower experiment), Spectrum is consistent with the background expectations
Detector characterization and first physics resultsDataset 2 : 0νββ analysis
Energy [keV]2400 2450 2500 2550 2600 2650 2700
Eve
nts [
coun
ts / k
eV]
02468
1012141618 Blinded
UnblindedTl208
Bi214 Co60
CUORE Preliminaryyr⋅Exposure: 38.1 kg
ROI Fit to evaluate best fit decay rate for 130Te: Simultaneous unbinned extended maximum likelihood fit ROI region: [2465,2575 keV] around Qββ (130Te). The fit has 3 components: • a posited peak at the Q-value of 130Te • a floating peak to account for the 60Co sum gamma line (2505 keV)• a constant continuum background, attributed to multi scatter Compton events from 208Tl and surface alpha events
- Overall signal efficiency: (55.3 ± 3.0)% - ROI background index: (9.8–1.5+1.7) × 10-3 c/(keV⋅kg⋅yr) - Half-life limit (90%C.L including syst.): T0ν (130Te) > 4.5 x 1024 yr
Detector characterization and first physics resultsDataset 2: Background spectrum - NLL FITBest fit decay rate (-0.03–0.04+0.07 (stat.) ± 0.01 (syst.)) × 10-24 / yr
Bayesian Half-life limit (90%C.L including syst.): T0ν > 4.5 x 1024 yr
Median expected sensitivity based on actual exposure: S0ν > 3.6 × 1024 yr (with sensitivity paper technique) S0ν >3.3 × 1024 yr (with same fit technique as ROI fit)