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Study of 48 Ca Double Beta Decay by CANDLES

Study of 48 Ca Double Beta Decay by CANDLES. T. Kishimoto Osaka Univ. Why 48 Ca. Highest Q value (4.27 MeV) next largest 150 Nd (3.3 MeV) Large phase space factor Little BG （ natural radioactivity g : 2.6 MeV, b : 3.3 MeV ） Natural abundance: 0.187% Huge amount of CaF 2 crystals

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Study of 48 Ca Double Beta Decay by CANDLES

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  1. Study of 48Ca Double Beta Decay by CANDLES T. Kishimoto Osaka Univ.

  2. Why 48Ca • Highest Q value (4.27 MeV) • next largest 150Nd (3.3 MeV) • Large phase space factor • Little BG（natural radioactivity g: 2.6 MeV, b: 3.3 MeV） • Natural abundance: 0.187% • Huge amount of CaF2 crystals • Isotope separation: expensive (no Gas) • Early studies (recent studies use separated isotope) • Next generation • Mn ~ T-1/2 ~ M-2(no BG) ~ M-4（BG limited） • 48Ca (no BG) NPA 730　’04, 215

  3. Double Beta Decay of 48Ca Studied by ELEGANT VI 1.76 y 0.63 y BG (sim) 4104 - 4438 keV 0nbb window 2nbb(sim) Yet no BG Not limited by backgrounds But only 6.4g of 48Ca NPA 730　’04, 215

  4. CANDLES CAlcium fluoride for studies of Neutrino and Dark matrters by Low Energy Spectrometer • CaF2(Pure) • 200kg, 300kg, 3t,30t(2%) • 48Ca (200g, 300g, 3kg, 300kg) • Liquid Scintillator • Wave Length Shifter • 4 p Active Shield • Passive shield • Photomultiplier • energy resolution Liquid Scintillator (Veto Counter) CaF2(Pure) Buffer Oil Large PMT

  5. CANDLES IRejection of ext. BG ADC(fast) ADC(total) CANDELS I POP detector Liquid Scintillator Liquid Scintillator CaF2 CaF2 ADC(total) 21COE Sep 11, Osaka

  6. Background @ Q value region • No natural BG @ ~4 MeV • Maximum energy • g~ 2.6 MeV, b~3.3 MeV, a~2.5 MeV(quench~0.3) • Successive decay of a b g • ~1msec decay time 212Bi (b) 212Po (a) Pulse shape • 100MHz FADCDT >30ns(3ch) ; ~5% • 500MHz FADC (under preparation) DT> 5ns ; ~1%

  7. Pulse Shape Discrimination Difference in decay time between a and g rays • PSD (Event by Event) • FADC (100MHz) • Afast/Aslow (Fast and slow component) • Discrimination between a and g(b) Events • Background Reduction ~ 0.3%

  8. Development of Low Radioactive CaF2 • b-a, a-a delayed coincidence • @ Oto Cosmo observatory 3t 600k 300k 95 crystals Number of CaF2 crystals U~36mBq/kg 14 (best) Th~20mBq/kg 6 (best) mBq/kg

  9. CaF2(Pure) CaF2 Emission (~285nm) Conversion by WLS(350~400nm) propagate PMT Energy resolution and BG rejection (2 phase) • CaF2: UV region (PMT) • Conversion layer • UV→visible (PMT) • UV transparent • Veto layer • Liq scint： absorb UV 137Cs (662keV) 9.14%(FWHM) Counts Energy (keV)

  10. CANDLES III (prototype) 10cm3 x 56 CaF2 f2800×h2600 21COE Sep 11, Osaka

  11. CANDLES III Photomultiplier Tube(13inch) • Inside View Tank for Liquid Scintillator (Acrylic Case) 40 PMTs Version Buffer water

  12. Test measurement just started @ Osaka (sea level) 1st 2nd no crystals Crystal with huge BG 5th 4th 3rd 2007/03/25 日本物理学会春の大会＠首都大学東京

  13. Mile stone • ELEGANTS VI • running with new BG rejection (2n) • CANDLES I, II • CANDLES III • 10cm3 cube (100 crystals) ~0.5 eV • BG of CaF2 ~30 Bq/kg (<100 Bq/kg ) • CANDLES III(UG) • CANDLES IV • 10cm3 cube (1000 crystals) 3.2t • BG of CaF2 ~10 Bq/kg for 0.2 eV • Kamioka Achieved Kamioka

  14. New experimental Hall under excavation XMASS KamLand CANDLES SK DUSEL town meeting Nov. 2-4, Washington DC

  15. Future • CANDLES V to sense ~10 meV region • ~30 ton CaF2 and 2% enrichment • Further large space • Kamland, SNO (Vessel and PMT’s) • DUSEL • Isotope enrichment • Available: 76Ge, 100Mo, 128Te • exception: 48Ca, 150Nd • R&D in progress • Crown ether (Resin is made) • Current separation constant is a bit low.

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