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Technische Universität München

Inorganic Scintillators for Rare Event Searches

M. v. Sivers, JAPS 15.11.2013


Rare Event Searches with ScintillatorsExperiment Scintillator Physics Technique Status SiteCRESST-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



Standard Scintillation Detectors vs. Bolometers

• Standard scintillation detector– Crystal at RT, scintillation light

detected by PMT– Particle identification by

pulseshape possible

• 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


Crystal PMT

e--recoils

O-recoils


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- 4274keV46Ca 0.004% 2β- 988keV40Ca 96.9% 2EC 194keV180W 0.13% 2EC 144keV186W 28.4% 2β- 490keV


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)


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



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



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 But no model-independent check of signal with same target material up to now


DAMA

NAIAD

Eur. Phys. J. C, 67:39-49 (2010) Phys. Lett. B 616:17-24 (2005)


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


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

http://arxiv.org/abs/1308.3478


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


CsI(Tl) Crystals• High Light Yield: 60,000ph/MeV• 127I, 133Cs: Good sensitivity for coherent scattering and spin-dependent

interactions• Pulseshape discrimination possible


@3keV


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)


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



Decay mode

Q-value

46Ca 0.004% 2β- 988keV40Ca 96.9% 2EC 194keV


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


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


alphasgammas


Decay mode

Q-value

64Zn 49.2% 2EC, ECβ+ 1096keV70Zn 0.61% 2β- 999keV74Se 0.89% 2EC, ECβ+ 1210keV


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:1303.4080Astropart. Phys. 34:344-353 (2011)




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)



Decay mode

Q-value

64Zn 49.2% 2EC, ECβ+ 1096keV70Zn 0.61% 2β- 999keV92Mo 14.8% 2EC, ECβ+ 1659keV


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



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



Decay mode

Q-value

46Ca 0.004% 2β- 988keV40Ca 96.9% 2EC 194keV92Mo 14.8% 2EC, ECβ+ 1659keV


AMORE• Search for 0ν2β with 40Ca100MoO4 scintillating bolometers (depleted in 48Ca)

– Discrimination of alphas with phonon-light technique and PSD– Good energy resolution ([email protected])

• Sensitivity goal <mν>=20-60meV: 250kg yrs exposure• Possibility to also search for Dark Matter (AMORE-DARK)


See talk by Y. Kim at RPScint13


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)
