Daniel Lenz, University of Wisconsin, Madison11/05/2010 - APS DNP
Cryogenic search for neutrinoless double beta decay
Daniel Lenz on behalf of the CUORE collaboration
Daniel Lenz, University of Wisconsin, Madison11/05/2010 - APS DNP
Motivation – 0νββ
ν ≠ ν ν = ν
• 0νββ is only experimentally feasible way to distinguish Dirac vs. Majorana neutrinos
• if 0νββ observed:
?
• lepton number violationΔL = 2
• Schechter-Valle theoremν = ν
• hint for seesaw type 1
mν = mD2 / MR << mD
• possible to determine absolute ν mass scale and ν hierarchy
n p
n
ν = ν e-
e-
p
0νββ-decay
0νββ2νββ
n
e-
e-
p
n p
νν
2νββ-decay
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Daniel Lenz, University of Wisconsin, Madison11/05/2010 - APS DNP
Bolometric Approach
• rise time: ~ 50 ms
• total pulse length several seconds
GE
• decay constant: ~ 200 ms
• several techniques employed to search for 0νββ
• here: bolometric approach
• several isotopes can be used
• large masses
• all energy measured in form of heat
• source = detector
• no event topology
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typical pulse shape parameters for large bolometers:
ΔT = E/C
• pulse shapes help identifying fake signals, e.g. electronics noise
Daniel Lenz, University of Wisconsin, Madison
CUORE Experiment
3m
80cm
• Cryogenic Underground Observatory for Rare Events
LNGS
• it is all about reducing background:
• only radiopure material copper, teflon
• goal: reach a flat bkg of 0.01 cts/(keV kg y) in ROI
• at least 36cm lead shields
• array of 988 bolometers19 towers, 13 planes4 bolometers /plane /tower
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• Borated polyethylene neutron shield
• located in Hall A of Gran Sasso National Lab (LNGS)
• overburden of ~3100 m.w.e. (relative to flat overburden) Phys.Rev. D73 053004
• total detector mass 741kg M(130Te) ~200 kg (130Te: 0νββ candidate isotope)
300 K
40 K
4 K
lead shield
0.7 K70 mK
10 mK
lead shield
+ external lead shield(not shown)
lead
sh
ield
cryogen-free dilution refrigerator
11/05/2010 - APS DNP
• demonstrated within factor 2 - 4
Daniel Lenz, University of Wisconsin, Madison11/05/2010 - APS DNP
• large bolometers 5 x 5 x 5 cm
• made from natural Te02
• 130Te abundance ~34 % (no enrichment)
• FWHM ~ 5 keV @2528 keV
CUORE Bolometers
Temperature sensor:
• NTD Ge thermistor
• resistance change converted into voltage pulse
• non-linear energy response
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Resolution:
high purity copper & Teflon holder structure
• Q-value (130Te) = 2528 keV
511 keVe+e-
583 keV208Tl
911 keV228Ac
965 + 969 keV 228Ac
1588228Ac
+ 1593 keV DEP 2104 keV
SEP
2615 keV208Tl
2528 keV0νββ
Phys. Rev. C 80 025501Phys. Rev. Lett. 102, 212502
Daniel Lenz, University of Wisconsin, Madison11/05/2010 - APS DNP
CUORE Calibration System see also poster 123 by Ian Guinn
• 12 source strings move under own weight 300K to 10mK without shifting detector base temperature
300 K
40 K
4 K
lead shield
0.7 K
70 mK
10 mK
lead shield
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• heat load requirements very strict: sources need to be at 4K
• dedicated thermalization mechanism currently tested
Kevlar string
copper capsuleswith Telfon
solenoid linear
actuator
pushing blade
iso view
• calibration is big challenge• slow detector response requires low activity sources (~100mBq)• large shielding & good self shielding requires sources inside detector array
• for bkg reasons sources have to be stored outside the cryostat
• each string has 30 copper crimps housing 232Th wire, calibrating 500keV - 3000keV
kevlar stringPTFE copper
capsule
thoriated tungsten wire
Daniel Lenz, University of Wisconsin, Madison11/05/2010 - APS DNP
Cuoricino
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• T0v1/2 (130Te) > 2.8 x 1024 y (90% C.L.)
(presented @ Neutrino 2010)
• mββ < 300 -700 meV (depending on choice of NME)
• M(Te02) = 40.7 kg => 130Te = 11.3 kg
44 crystals: 5cm x 5cm x 5cm (CUORE-type)
• Total exposure 19.75 kg • y
18 crystals: 3cm x 3cm x 6cm
• located at LNGS Hall A smaller cryostat, single tower
• Cryostat will be further used for CUORE-like tower assembly tests: CUORE-0
• b(ROI) = 0.169 ± 0.01 cts / (keV kg y)
• predecessor of CUORE using same experimental technique
4 are enriched
FWHM ~6 keV FWHM ~10 keV FWHM ~14 keV
• two independent analyses, US and Italy: (very similar, agreeing, results)
0νββ expected
Daniel Lenz, University of Wisconsin, Madison
CUORE Experiment - Status
• CUORE experimental hut finished
• cryostat main support in place
• 450 bolometers ready and stored underground at LNGS; tests ongoing
• 12/2010 outer cryostat vessels delivery
• US bolometer production started
• early 2011 cryostat 4K tests
• 12/2010 partial calibration system delivery
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• 2013 CUORE data taking
11/05/2010 - APS DNP
• fall 2011 CUORE-0 data taking
CUORE hut
cryostat main support
now:
• mid 2011 delivery dilution unit
bolometerspackaged
Daniel Lenz, University of Wisconsin, Madison11/05/2010 - APS DNP
Projected Sensitivity
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mββ = 41 – 96 meV (depending on NME)
• start probing inverted hierachyT0ν
1/2 = 1.5 x 1026 y at 1σCUORE Sensitivity at 1σ:
• 5 years live time and bkg of b = 0.01 cts/ (keV kg y)
Cuoricino 1σ result
CUORE-0 – 0.06 cts/(keV kg y)
Combined Cuoricino + CUORE-0CUORE – 0.01 cts/(keV kg y)
Daniel Lenz, University of Wisconsin, Madison11/05/2010 - APS DNP
Summary
• 0νββ is only experimentally feasible way to distinguish Dirac vs. Majorana neutrinos
• CUORE uses bolometers made of natural Te02 to search for 0νββ of 130Te
• Goal of background in ROI of 0.01 cts/(keV kg y); demonstrated within factor 2-4
• Good progress being made:
• CUORE-0 data-taking starts fall 2011• CUORE data-taking 2013
• CUORE sensitivity at 1σ T0ν1/2 = 1.5 × 1026 y => mββ = 41-96 meV
start probing inverted hierarchy
• calibration is challenging: 12 strings with 30 sources brought into cryostat from 300K to 10mK, without changing detector base temperature
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