technische universität münchen inorganic scintillators for rare event searches m. v. sivers, japs...

Technische Universität München

Inorganic Scintillators for Rare Event Searches

M. v. Sivers, JAPS 15.11.2013


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



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


CrystalPMT

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+ 1096keV

70Zn 0.61% 2β- 999keV

74Se 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)


technische universität münchen inorganic scintillators for rare event searches m. v. sivers, japs...

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