Technische Universität München
Inorganic Scintillators for Rare Event
Searches
M. v. Sivers, JAPS 15.11.2013
Technische Universität München
Rare Event Searches with Scintillators
Experiment
Scintillator
Physics
Technique
Status
Site
CRESST-II
CaWO4
Dark Matter
Bolometer
Running
LNGS, Italy
DAMA/LIBRA
NaI
Dark Matter
Standard
Running
LNGS, Italy
KIMS
CsI, NaI
Dark Matter
Standard
Running
Y2L, Korea
TEXONO
CsI
Neutrino physics
Standard
Running
KSNL, Taiwan
CANDLES
CaF2
0ν2β
Standard
R&D
Kamioka, Japan
DM-Ice
NaI
Dark Matter
Standard
R&D
South Pole
ANAIS
NaI
Dark Matter
Standard
R&D
LSC, Spain
KAMLAND-Pico
NaI
Dark Matter
Standard
R&D
Kamioka, Japan
SABRE
NaI
Dark Matter
Standard
R&D
LNGS,
Italy/SNOLab,
Canada (?)
LUCIFER
ZnSe
0ν2β
Bolometer
R&D
LNGS, Italy (?)
LUMINEU
ZnMoO4
0ν2β
Bolometer
R&D
LSM, France (?)
AMORE
CaMoO4
0ν2β, Dark
Matter
Bolometer
R&D
Y2L, Korea
M. v. Sivers, JAPS 15.11.2013
Technische Universität München
Standard Scintillation Detectors vs.
Bolometers
•
Standard scintillation detector
– Crystal at RT, scintillation light
detected by PMT
– Particle identification by
pulseshape possible
Crystal
PMT
•
Scintillating bolometer
– Crystal at mK temperature
equipped with thermal sensor
(phonon channel)
– Scintillation light detected by e.g.
Si/Ge waver with thermal sensor
(light channel)
– Particle identification by
light/phonon ratio
e--recoils
O-recoils
M. v. Sivers, JAPS 15.11.2013
Technische Universität München
CaWO4 Crystals
•
In house production at TUM since 2011
 Very good radiopurity was achieved: total α-activity (1-3mBq/kg)
•
•
Light Yield: 40% of NaI(Tl) at RT, 1.7x increase at low temperatures
Multi-material target for DM
– W (A=184): Good sensitivity for coherent scattering (σcoh~A2)
– Ca, O: Sensitivity to light WIMPs
– 183W (14%): some sensitivity to spin-dependent scattering
Isotope
Natural
abundance
Decay
mode
Q-value
48Ca
0.18%
2β-
4274keV
46Ca
0.004%
2β-
988keV
40Ca
96.9%
2EC
194keV
180W
0.13%
2EC
144keV
186W
28.4%
2β-
490keV
M. v. Sivers, JAPS 15.11.2013
Technische Universität München
CRESST-II
•
Dark Matter search with CaWO4 scintillating bolometers
 Discrimination between electron and nuclear recoils by phonon-light technique
•
Observation of 67 candidate events in 730kg days of data (2011)
 Maximum Likelihood analysis favored signal over background-only hypothesis
with significance >4σ
 But large contribution from background demands further clarification
Eur. Phys J. C,72:1971 (2012)
M. v. Sivers, JAPS 15.11.2013
Technische Universität München
CRESST-II
•
New run started July 2013
 Detector mass doubled
 Improved background situation due to cleaner materials and new detector
designs
•
Analysis for double beta processes and low-threshold Dark Matter analysis
ongoing
M. v. Sivers, JAPS 15.11.2013
Technische Universität München
NaI(Tl) Crystals
•
•
•
•
•
Most commonly used scintillator  established technique
High Light Yield (≈45,000ph/MeV)
23Na (100%): Sensitivity for light WIMPs and spin-dependent interactions
127I (100%): Good sensitivity for coherent scattering and spin-dependent
interactions
Main background for Dark Matter search: 3keV x-ray from EC decay of
40K
M. v. Sivers, JAPS 15.11.2013
Technische Universität München
DAMA/LIBRA
•
Dark Matter search with 250kg of NaI(Tl)
– 2keV threshold (5.5-7.5phe/keV), background rate 1cpd/keV/kg (13ppb of natK)
– Positive signal for annual modulation with 8.9σ measured over 13 annual
cycles
– Fit to rate of single hits between 2-6keV with Acos[ω(t-t0)] gives
A=(0.0116±0.0013)cpd/kg/keV, ω=(0.999±0.002)yr, t0=(146±7)d
(t0=152.5d expected for DM)
– No modulation in multiple hits, no modulation above 6keV
– WIMP parameter space excluded by several other experiments
Eur. Phys. J.
C, 67:39-49
(2010)
Phys. Lett.
B 616:17-24
But
no model-independent
check of signal with same target
material
up to(2005)
now
NAIAD
DAMA
M. v. Sivers, JAPS 15.11.2013
Technische Universität München
DM-Ice
•
250kg of NaI(Tl) deployed in IceCube detector
– Goal: Check DAMA claim on southern hemisphere
– 17kg of NAIAD crystals as prototype running since 2011
• Current background 7x higher then DAMA (650ppb natK)
 R&D for crystal growth ongoing, pushing threshold below 4keV
Astropart. Phys. 35 (2012) 749-754
M. v. Sivers, JAPS 15.11.2013
Technische Universität München
ANAIS
•
Dark Matter search with 250kg of NaI(Tl)
– 25kg prototype running since Dec. 2012
 40ppb of natK (3x higher than DAMA)
 High light collection 12-16phe/keV without lightguides (2x higher than DAMA)
 R&D on crystal growth ongoing (goal <20ppb natK)
arXiv:1308.3478
M. v. Sivers, JAPS 15.11.2013
Technische Universität München
SABRE
•
Dark Matter search with 100kg of NaI(Tl) crystals in liquid scintillator (LAB) veto
–
–
–
–
Purchased 8kg of NaI powder with 12ppb/3.5ppb natK
First step: measure 40K concentration in crystals with liquid scintillator coincidence
Second step: Move chamber to LNGS or SNOLab for DM run
Expected background rate 0.39cpd/kg/keV (2.5x lower than DAMA)
See Talk by E. Shields at TAUP2013
M. v. Sivers, JAPS 15.11.2013
Technische Universität München
CsI(Tl) Crystals
•
•
•
High Light Yield: 60,000ph/MeV
127I, 133Cs: Good sensitivity for coherent scattering and spin-dependent
interactions
Pulseshape discrimination possible
@3keV
M. v. Sivers, JAPS 15.11.2013
Technische Universität München
KIMS
•
Dark Matter search with 100kg of CsI(Tl)
– Light yield 5phe/keV, background rate 2-4cpd/kg/keV
– Total exposure 24.5ton days
– Excludes DAMA signal as WIMP scattering on iodine
•
Annual modulation analysis with 2.5years (75.5ton days) data
– amplitude <0.0122cpd/kg/keV at 90%CL (DAMA signal 0.0116±0.0013 cpd/kg/keV)
PRL 108, 181301 (2012)
M. v. Sivers, JAPS 15.11.2013
Technische Universität München
CaF2 Crystals
•
•
Light Yield: 24,000ph/MeV (CaF2(Eu))
48Ca (0.18%): 0ν2β candidate with highest Q-value (4.27MeV)
– Enrichment difficult (no gaseous Ca compunds): 1g of 48Ca costs $100k
•
•
19F
(100%): Sensitivity to spin-dependent interactions
Pulseshape discrimination possible
Isotope
Natural
abundance
Decay
mode
Q-value
46Ca
0.004%
2β-
988keV
40Ca
96.9%
2EC
194keV
M. v. Sivers, JAPS 15.11.2013
Technische Universität München
CANDLES III
•
Search for 0ν2β with 305kg CaF2(pure) in liquid scintillator veto
– Best limit on 0ν2β of 48Ca from predecessor ELEGANT VI (exposure
4.23kg yrs): T1/2>1.4e22y (Nucl. Phys. A 730 (2004) 215–223)
– R&D on enrichment of 48Ca: chemical processing with crown ether, Laser
separation
See talk by Umehara at TAUP2013
M. v. Sivers, JAPS 15.11.2013
Technische Universität München
ZnSe Crystals
•
•
•
•
•
82Se
(7.8%): Candidate for 0ν2β (Q-value 2996keV)
High radiopurity: 17μBq/kg (226Ra, 232Th)
Light Yield at low temperature: 7.4keV/MeV (CaWO4: 20keV/MeV)
Pulseshape discrimination possible
Inverse quenching factor (LYα/LYγ=4.2) not yet understood
alphas
gammas
Isotope
Natural
abundance
Decay
mode
Q-value
64Zn
49.2%
2EC, ECβ+
1096keV
70Zn
0.61%
2β-
999keV
74Se
0.89%
2EC, ECβ+
1210keV
M. v. Sivers, JAPS 15.11.2013
Technische Universität München
LUCIFER
•
Search for 0ν2β with Zn82Se scintillating bolometers
– Good energy resolution (13keV@2615keV)
– Discrimination of alphas with phonon-light technique and PSD
•
•
Sensitivity goal of <mν>=100meV: 10kg of 95% enriched 82Se, 5 years
exposure, <10-3 counts/kg/keV/y, 5keV resolution
Possibility to also search for DM
arXiv:1303.4080
Astropart. Phys. 34:344-353 (2011)
M. v. Sivers, JAPS 15.11.2013
Technische Universität München
ZnMoO4 Crystals
•
•
•
100Mo
(9.6%): Candidate for 0ν2β (Q-value 3034keV)
Low Light Yield at low temperatures: 1keV/MeV
High radiopurity: <32μBq/kg (226Ra, 228Th)
Isotope
Natural
abundance
Decay
mode
Q-value
64Zn
49.2%
2EC, ECβ+
1096keV
70Zn
0.61%
2β-
999keV
92Mo
14.8%
2EC, ECβ+
1659keV
M. v. Sivers, JAPS 15.11.2013
Technische Universität München
LUMINEU
•
Search for 0ν2β with Zn100MoO4 scintillating bolometers
– Good energy resolution (5.7keV@2615keV)
– Discrimination of alphas with phonon-light technique and PSD (discr. power 20σ!)
•
•
•
Sensitivity goal of <mν>=100meV: 30kg of 90% enriched detectors, 5 years
exposure, ≈1.5*10-3 counts/kg/keV/y, 5keV resolution
Main background from pileup of 2ν2β: development of faster detectors
Collaboration with TUM to grow high purity ZnMoO4 crystals
arXiv:1202.0238
M. v. Sivers, JAPS 15.11.2013
Technische Universität München
CaMoO4 Crystals
•
•
•
•
Highest Light Yield among molybdates: 30,000ph/MeV (at low temp.)
For 0ν2β of 100Mo (Q-value 3034keV) 2ν2β of 48Ca (Q-value 4270keV)
serves as background
High radiopurity: ≈80μBq/kg (226Ra, 228Th)
Pulseshape discrimination possible
Isotope
Natural
abundance
Decay
mode
Q-value
46Ca
0.004%
2β-
988keV
40Ca
96.9%
2EC
194keV
92Mo
14.8%
2EC, ECβ+
1659keV
M. v. Sivers, JAPS 15.11.2013
Technische Universität München
AMORE
•
Search for 0ν2β with 40Ca100MoO4 scintillating bolometers (depleted in 48Ca)
– Discrimination of alphas with phonon-light technique and PSD
– Good energy resolution (11.2keV@5.5MeV)
•
•
Sensitivity goal <mν>=20-60meV: 250kg yrs exposure
Possibility to also search for Dark Matter (AMORE-DARK)
See talk by Y. Kim at RPScint13
M. v. Sivers, JAPS 15.11.2013
Technische Universität München
Summary
•
Inorganic scintillators
– Key properties for rare event searches: Radiopurity, Light Yield
– Advantages:
• Wide choice of materials
• Multimaterial approach:
– Simultaneous sensitivity to spin-dependent and coherent interactions/light and heavy
WIMPs
– Possibility to study many rare decays in one experiment (e.g. 2β, 2EC, ECβ+, …)
– Disadvantages:
• Crystal growth is extensive, especially for ton-scale experiments
• No purification possible after crystal growth
•
Scintillating bolometers
– Very good energy resolution
– Active background discrimination with phonon-light technique
– Promising for next generation 0ν2β experiments (zero background seems feasible)
M. v. Sivers, JAPS 15.11.2013