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I norganic Scintillators for Rare Event Searches

I norganic Scintillators for Rare Event Searches. Rare Event Searches with Scintillators. Standard Scintillation Detectors vs. Bolometers. Standard scintillation detector Crystal at RT, scintillation light detected by PMT Particle identification by pulseshape possible.

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I norganic Scintillators for Rare Event Searches

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  1. Inorganic Scintillators for Rare Event Searches M. v. Sivers, JAPS 15.11.2013

  2. Rare Event Searches with Scintillators M. v. Sivers, JAPS 15.11.2013

  3. 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 M. v. Sivers, JAPS 15.11.2013

  4. 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 M. v. Sivers, JAPS 15.11.2013

  5. CRESST-II • Dark Matter search with CaWO4scintillating 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

  6. 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

  7. 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

  8. 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 Eur. Phys. J. C, 67:39-49 (2010) Phys. Lett. B 616:17-24 (2005) NAIAD DAMA M. v. Sivers, JAPS 15.11.2013

  9. 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

  10. 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

  11. 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

  12. 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

  13. 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

  14. CaF2 Crystals • Light Yield: 24,000ph/MeV (CaF2(Eu)) • 48Ca (0.18%): 0ν2β candidate with highest Q-value (4.27MeV) • Enrichment difficult (no gaseous Cacompunds): 1g of 48Ca costs $100k • 19F (100%): Sensitivity to spin-dependent interactions • Pulseshape discrimination possible M. v. Sivers, JAPS 15.11.2013

  15. 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

  16. 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 M. v. Sivers, JAPS 15.11.2013

  17. 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, <10-3counts/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

  18. 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) M. v. Sivers, JAPS 15.11.2013

  19. LUMINEU • Search for 0ν2β with Zn100MoO4scintillating 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

  20. CaMoO4 Crystals • Highest Light Yield among molybdates: 30,000ph/MeV (at low temp.) • For 0ν2βof 100Mo (Q-value 3034keV) 2ν2β of 48Ca (Q-value 4270keV) serves as background • High radiopurity: ≈80μBq/kg (226Ra, 228Th) • Pulseshape discrimination possible M. v. Sivers, JAPS 15.11.2013

  21. AMORE • Search for 0ν2β with 40Ca100MoO4scintillating 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

  22. 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

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