Post on 28-Dec-2015
First neutrinoless double beta decay results from CUORE-0
L. Gironi on behalf of the CUORE collaboration
Università degli Studi di Milano - BicoccaINFN di Milano - Bicocca
10th M E D E X '15 meetingPrague, June 09th - 12th, 2015
Luca Gironi Prague, June 09th - 12th, 2015
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
- Possibility to choose among all the ββ isotope
- Q-value in low background region
- Very low background level already reached but
surface contaminations
Bolometers for 0νDBD
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Why bolometers are suitable detectors for 0νDBD ?
TNT 0
TMaT 00B
0 BTM
0 BTM
BTM
TMaTB
0
abundance isotopic
efficiency detector
[keV] resolution energyy][c/keV/kg/ background B
[kg] mass detector
[y] time live
a
M
T
TMa
Luca Gironi Prague, June 09th - 12th, 2015
TeO2 Bolometric DetectorsAt 10 mK, energy deposited in TeO2 results in a measurable change in temperature
Energy release → ΔT→ ΔR in the thermistor → ΔV
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
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ΔTtherm~ 10-20 μK/MeVΔTcryst ~ 0.1 mK/MeV
ΔRtherm ~ 3 MΩ/MeVΔVtherm ~ 0.3 mV/MeV
Luca Gironi Prague, June 09th - 12th, 2015
The CUORE program
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Cuoricino2003-2008
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.)
B
TMTB
0
CUORE2015-2020
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.)
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)
Luca Gironi Prague, June 09th - 12th, 2015
Cuoricino
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)
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62 TeO2 crystals (40.7 kg) operated at Gran Sasso (2003-2008)
• M· T (130Te): 19.75 kg.yr• ∆: 6.3 ± 2.5 keV FWHM• B: 0.169 ± 0.006 c/keV/kg/yr
T1/2 > 2.8 x 1024 y (90% C.L.)
0νββ upper limit
Luca Gironi Prague, June 09th - 12th, 2015
Qββ
Cuoricino – Background
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α
α
Main sources of background in the ROI:
β/γ events α eventsQββ
30% Compton from 208Tl decays in cryostat60% Degraded alphas on copper surfaces10% Degraded alphas on crystal surfaces
Physics dataCalibration data
Luca Gironi Prague, June 09th - 12th, 2015
CUORE-0
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
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Luca Gironi Prague, June 09th - 12th, 2015
CUORE/CUORE-0 – Assembly line
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Clean Room for Detector Assembly and Storage
CUORE hutCuoricino/
CUORE-0 hut
CUORE-0 construction was carried out inside N2-flushed glove boxes in CUORE hut’s clean room.
Luca Gironi Prague, June 09th - 12th, 2015 9
CUORE/CUORE-0 – Assembly lineSemi-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
Luca Gironi Prague, June 09th - 12th, 2015 10
CUORE/CUORE-0 – Assembly lineTower 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
Luca Gironi Prague, June 09th - 12th, 2015 11
CUORE/CUORE-0 – Assembly lineConnection to readout: Wire bonding
• All wire-bonding done in N2 flushed glove box
• Vertical bonding machine with auxiliary X-Y motion
Luca Gironi Prague, June 09th - 12th, 2015
CUORE-0with 10mK shield
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CUORE/CUORE-0 – Assembly line
The successful operation of CUORE-0 demonstrated the validity of the CUORE tower assembly line and of the CUORE cleaning procedures.
CUOREtower
Tower storage
Luca Gironi Prague, June 09th - 12th, 2015 13
CUORE-0
• Uses the old Cuoricino cryostat
• Electronics from Cuoricino
• Shielding from Cuoricino
• Cooled to base T (~10 mK) Mar 2013
Luca Gironi Prague, June 09th - 12th, 2015
CUORE-0 – Data taking• M· T (130Te): 9.8 kg· yr of 130Te
• 51/52 NTDs online
• 50/52 heaters online
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Calibration data taking
Physics data taking
1st
cam
paig
n2
nd c
am
paig
n
Luca Gironi Prague, June 09th - 12th, 2015 15
Total fit on the 2615 keV lineDistribution of energy resolution @ 2615
keV
CUORE-0 – Calibration energy resolution
The 5 keV CUORE goal has been
reached
CUORE-0Preliminary
CUORE-0Preliminary
Exposure-weightedHarmonic Mean
FWHM
RMS ofFWHM
Cuoricino 5.8 keV 2.1 keV
CUORE-0 4.9 keV 2.9 keV
Luca Gironi Prague, June 09th - 12th, 2015
CUORE-0 – Background
• 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)
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Comparison of the total background spectrum in CUORE-0 and Cuoricino
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
CUORE-0 Preliminary
Luca Gironi Prague, June 09th - 12th, 2015
CUORE-0 – 0νDBD analysisData processing and analysis techniques are focused to the correct reconstruction of each eventenergy (optimal filtering technique) and eventually to the creation of the energy spectrum of the ROI:
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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)%
Luca Gironi Prague, June 09th - 12th, 2015
CUORE-0 – 0νDBD searchAfter all cuts: 233 events in ROI [2470-2570 keV].
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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
We find no evidence for a signal and set 90% C.L. lower limit from profile likelihood:
yrT 241072 .01/2
Pro
file
neg
ati
ve log
-lik
elih
ood
CUORE-0 PreliminaryCUORE-0 Preliminary
Luca Gironi Prague, June 09th - 12th, 2015 19
CUORICINO/CUORE-0 combined limitWe combine the CUORE-0 result with the existing 19.75 kg· yr of 130Te exposure from Cuoricino
yrT 241004 .01/2
This is the most stringent limit on this half-life !
Pro
file
negati
ve log-
likelih
ood
CUORE-0 Preliminary
Luca Gironi Prague, June 09th - 12th, 2015 20
Extrapolation to mββ
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)
CUORE-0 Preliminary
Luca Gironi Prague, June 09th - 12th, 2015
The CUORE program
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Cuoricino2003-2008
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.)
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)
B
TMTB
0
CUORE2015-2020
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.)
Luca Gironi Prague, June 09th - 12th, 2015
CUORE• 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):
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yrT 251059 .01/2
Luca Gironi Prague, June 09th - 12th, 2015
CUORE – Background mitigation efforts• Improve shielding and radio-purity of cryostat materials
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• 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
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)
Luca Gironi Prague, June 09th - 12th, 2015
CUORE – Self shielding
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• CUORE-0: All bolometers face 10 mK shield
• CUORE: Only outermost crystals face 10 mK shield
Luca Gironi Prague, June 09th - 12th, 2015
CUORE – Status
Assembly of the 19 CUORE towers is complete
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Expect to deploy the array in the cryostat later this year.
Luca Gironi Prague, June 09th - 12th, 2015
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
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Plan to start operations by end of 2015.
Cryostat Vessel Flanges
Diluition unitOutermost shield
Luca Gironi Prague, June 09th - 12th, 2015
The CUORE program
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Cuoricino2003-2008
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.)
CUORE2015-2020
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
Luca Gironi Prague, June 09th - 12th, 2015
Beyond CUORE
Next generation bolometric experiment for 0νββ searches aims to use active rejection techniques to drastically reduce the background:
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CUORE Upgrade with Particle ID (CUPID)
TMaT 00B
BTM
TMaTB
0
arXiv:1504.03599
Luca Gironi Prague, June 09th - 12th, 2015
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.
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Luca Gironi Prague, June 09th - 12th, 2015
The CUORE Collaboration
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