1. DPF-JPS 2006 Oct 31, Hawaii 1 CANDLES system for the study of 48-Ca double beta decay T. Kishimoto Osaka Univ.

2. DPF-JPS 2006 Oct 31, Hawaii 2 Why 48 Ca Highest Q value (4.27 MeV) –next largest 150 Nd (3.3 MeV) –Large phase space factor –Little BG （ natural radioactivity  : 2.6 MeV,  : 3.3 MeV ） Natural abundance: 0.187% –Isotope separation: expensive (no Gas) –Early studies (recent studies use separated isotope) Next generation –M ~ T -1/2 ~ M -2 (no BG) ~ M -4 （ BG limited ） – 48 Ca (no BG) NPA 730 ’04, 215

3. DPF-JPS 2006 Oct 31, Hawaii 3 How to sense m =10 -(1~2) eV Big detector –Huge amount of materials Low radioactive background –Active shield –Passive shield –Low background material –BG rejection by signal processing High resolution –Backgrounds from 2  decay CANDLES is our solution

4. DPF-JPS 2006 Oct 31, Hawaii 4 CANDLES CaF 2 (Pure) 200kg, 300kg, 6t,100t 48 Ca (200g, 300g, 6kg, 100kg) Liquid Scintillator Wave Length Shifter 4  Active Shield Passive shield Photomultiplier Photomultiplier energy resolution CaF 2 (Pure) Liquid Scintillator (Veto Counter) Buffer Oil Large PMT CAlcium fluoride for studies of Neutrino and Dark matrters by Low Energy Spectrometer

5. DPF-JPS 2006 Oct 31, Hawaii 5 CaF 2 crystal Big detector –Best optical lens –Long attenuation length 10m (catalog value for visible light) >1m (our measurement for scintillation light) CANDLES IV –15x15x15 cm 3 x 600 (6t) –Increase the number of nuclei ( 48 Ca) 6.4 g (ELE VI) ~6(kg)

6. DPF-JPS 2006 Oct 31, Hawaii 6 CANDLES I POP (Proof of Principle) Detector CaF 2 (pure) crystal in liquid scintillator (with w.l. shifter) viewed by 4 PMTs (5 inch) liq. scint. : mineral oil + DPO (3 g/l) + Bis-MSB (0.3 g/l)

7. DPF-JPS 2006 Oct 31, Hawaii 7 Signal discrimination ~1 liquid scintillator ~0.04 CaF 2 Liquid Scintillator CaF 2 ADC(fast)/ADC(total) Decay time Liq. Scinti ~10 nsec CaF 2 ~1  sec

8. DPF-JPS 2006 Oct 31, Hawaii 8 Signal discrimination Co source 57 Co source ADC(fast)/ADC(total) ADC(total) Signal from Liquid scintillator CaF 2

9. DPF-JPS 2006 Oct 31, Hawaii 9 Background @ Q value region No natural BG @ ~4 MeV –Maximum energy  ~ 2.6 MeV,  ~3.3 MeV,  ~2.5 MeV(quench~0.3) –Successive decay of  ~1  sec decay time E max =5.8MeV(U) 5.3MeV(Th)  Pulse shape Gate width( 4  sec )

10. DPF-JPS 2006 Oct 31, Hawaii 10 Reduction 100MHz FADC  T > 30ns(3ch) ; ~5% 500MHz FADC (under preparation)...  T > 5ns ; ~1% Rejection of Double Pulse Prompt Delayed Typical Pulse Shape(100MHz FADC) 900ns 50ns 212 Bi 212 Po T 1/2 = 0.299  sec 64% Q  = 8.95MeV Q  = 3.27MeV Q  = 2.25MeV Q  = 7.83MeV  

11. DPF-JPS 2006 Oct 31, Hawaii 11 Pulse Shape Discrimination PSD (Event by Event)PSD (Event by Event) –FADC (100MHz) –A fast /A slow (Fast and slow component ) Difference in decay time between  and  rays Discrimination between  and  Events Background Reduction ~ 0.3%

12. DPF-JPS 2006 Oct 31, Hawaii 12 Development of High Purity CaF 2 Crystals Radioactivities in CaF 2 (pure) Crystal (  delayed coincidence) Radioactivities in CaF 2 Powder (HPGe measurement) U-chain( 214 Bi) ~36  Bq/kg … 1/30 of Previous Crystals Th-chain( 220 Rn) ~28  Bq/kg … 1/3 of Previous Crystals CaF 2 Powder Fused CaF 2 Raw Materials CaCO 3, HF CaF 2 Crystal Powder selection Crystal growing CaF 2 (Eu) in ELEGANT VI U-chain( 214 Bi) : 1100  Bq/kg Th-chain( 220 Rn) : 98  Bq/kg 96 crystals U and Th (ICP-MS)

13. DPF-JPS 2006 Oct 31, Hawaii 13 Radioactivities in CaF 2  delayed coincidence @ Oto Cosmo observatory U~36  Bq/kg 14 (best) Th~20  Bq/kg 6 (best) Number of CaF 2 crystals mBq/kg 95 crystals

14. DPF-JPS 2006 Oct 31, Hawaii 14 Energy resolution of CaF 2 Energy Resolution Scintillation light –~0.5 of CaF 2 (Eu) (quart window PMT) –peak emission U.V. (285 nm) Increase # of photons –Wavelength shifter – UV visible light

15. DPF-JPS 2006 Oct 31, Hawaii 15 Two Phase System CaF 2 (Pure) Concept of Method Conversion Phase –Large conversion eff. –good transparency for UV Veto Phase –Large light output with aromatic solvent CaF 2 Emission (~285nm) Conversion by WLS(350~400nm) PMT propagate UV light Visible light High resolution and High veto efficiency

16. DPF-JPS 2006 Oct 31, Hawaii 16 Energy resolution Side View 9.14%(FWHM) Energy (keV) Counts Energy (keV) 60 Co (1333keV) 5.91%(FWHM) 137 Cs (662keV) CaF 2 (pure) Liquid Scintillator Standard  Source CANDLES I with 10 cm 3 CaF 2 (pure) (WLS phase) Energy Resolution: 9.1%(FWHM) at 662keV =3.4% (FWHM) at 4.27MeV Req. for CANDLES III ; 4.0% ~1 ph/keV

17. DPF-JPS 2006 Oct 31, Hawaii 17 H2OH2O 15”PMT Mount System CaF2(Pure) 10cm cube Liquid Scintillator CANDLES-II Prototype 45cm Cosmic-ray Events (High Energy) Index 1.44@586nm (CaF 2 ) Index 1.46@586nm (Mineral Oil) S.Umehara

18. DPF-JPS 2006 Oct 31, Hawaii 18 CANDLES III Construction almost completed @ Osaka Univ. CaF 2 (pure) –60×10 3 cm 3 ; 191 kg Liquid scintillator –  1m× h 1m acrylic container Purification system H 2 O Buffer: passive shield –   00× h 2600 –safety regulation PMTs –15 ” PMT (×8) : R2018 –13 ” PMT (×32) : R8055

19. DPF-JPS 2006 Oct 31, Hawaii 19 CANDLES III (prototype)  2.8 m h  2.6 m

20. DPF-JPS 2006 Oct 31, Hawaii 20 CANDLES III Inside View Photomultiplier Tube(13inch) Tank for Liquid Scintillator (Acrylic Case) 40 PMTs Version And 60 PMTs Version... Funded

21. DPF-JPS 2006 Oct 31, Hawaii 21 LS tank 4 CaF 2 modules installed Access port for calibration

22. DPF-JPS 2006 Oct 31, Hawaii 22 CaF 2 module CaF 2 + conversion phase + acrylic case half filled filled Index 1.44@586nm (CaF 2 ) Index 1.46@586nm (Mineral Oil)

23. DPF-JPS 2006 Oct 31, Hawaii 23 CANDLES III(U.G.) CaF 2 (pure) –10 3 cm 3 × 96 crystals; 305 kg Liquid scintillator –two phase system –Purification system H 2 O Buffer –passive shield PMTs –17 ” PMT (×14) : R7250 –13 ” PMT (×56) : R8055 –mirror type reflector photon trans. simulation energy res. ~3.5 % @ Q  Kamioka underground lab. san-chika

24. DPF-JPS 2006 Oct 31, Hawaii 24 CANDLES IV CaF 2 (Pure) Liquid Scintillator (Veto Counter) Buffer Oil Large PMT 15×15×15 cm 3 CaF 2 (600 cubes) 6.4 t liquid scintillator Vessel ( 48 Ca) 6.4 kg 1.BG (~3  Bq/kg Th) 1.Needs R&D 2.Current best ~6  Bq/kg 2.Energy resolution 1.Photo coverage

25. DPF-JPS 2006 Oct 31, Hawaii 25 Mile stone ELEGANTS VI –running with new BG rejection (2 ) CANDLES I, II CANDLES III –10cm 3 cube (100 crystals) ~0.5 eV –BG of CaF 2 ~30  Bq/kg CANDLES III(UG) CANDLES IV –15cm 3 cube (600 crystals) 6t –BG of CaF 2 ~3  Bq/kg for 0.1 eV –Kamioka Achieved Kamioka

26. DPF-JPS 2006 Oct 31, Hawaii 26 Future CANDLES V to sense 30 meV region –~100 ton CaF2 –Can be installed in Kamland SNO Isotope separation –Available: 76 Ge, 100 Mo, 128 Te –exception: 48 Ca, 150 Nd (feasible?) R&D –Crown ether, centrifuge, others If 2%: 10 meV region Vessel and PMT’s

27. DPF-JPS 2006 Oct 31, Hawaii 27 Sensitivity of CANDLES Series CANDLES III Performance @ sea Level Lab. Now 2006 2007 2008 Measurement @ Underground Lab. CANDLES IVConstruction start CANDLES III 3.2kg×60 crystals 191kg 4.0%(Req.) 50 20 0.01 0.07 0.04 0.14/year 5 years 0.56 eV CANDLES IV 6.4 ton 3.5%(Req.) 10 1 0.10 0.03 0.10 0.06 0.29/year 6 0.10 CANDLES V 100 ton 3.2%(Req.) 1 0.1 1.33 0.05 0.15 0.10 1.63/year 7 0.03 Crystal Total Mass Energy Resolution 214 Bi(  Bq/kg) 212 Bi(  Bq/kg) 2  214 Bi 212 Bi 208 Tl Expected BG Measuring Time