1. June 5 2007INPC20071 Study of 48 Ca double beta decay with CANDLES OGAWA Izumi ( 小川 泉 ) Osaka Univ. ( 大阪大学 )

2. June 5 2007 INPC20072 Double beta decay of 48 Ca Largest Q value (4.27 MeV) next largest; 150 Nd (3.3 MeV) large phase space factor almost background free (  : 2.6 MeV,  : 3.3 MeV) Low Natural abundance → 0.187% large detector enrichment Next generation detector M det 2 if background free M det 4 if background limited

3. June 5 2007 INPC20073 CANDLES CAlcium fluoride for studies of Neutrino and Dark matters by Low Energy Spectrometer undoped CaF 2 (CaF 2 (pure)) 48 Ca ( Q  =4.27 MeV ) 300 kg 3 t 100 t Liquid Scintillator (LS) 4  active shield Passive shield wavelength shifter for CaF 2 Photomultiplier large photo-caoverage

4. June 5 2007 INPC20074 CANDLES I - POP (Proof of Principle) Detector CaF 2 (pure) crystal in liquid scintillator (with w.l. shifter) viewed by 4 PMTs (5 inch) LS : mineral oil + DPO (3 g/l) + Bis-MSB (0.3 g/l) 4  active shield

5. June 5 2007 INPC20075 Performance Test (4  active shield) events from LS events from CaF 2 Clear separation between CaF 2 and LS 2 ADCs with different gate width 40 K

6. June 5 2007 INPC20076 Energy resolution Side View 9.14%(FWHM) Energy (keV) Counts Energy (keV) 60 Co (1333 keV) 5.91%(FWHM) 137 Cs (662 keV) CaF 2 (pure) wavelength shifter Standard  Source CANDLES I with 10 cm 3 CaF 2 (pure) Energy Resolution: 9.1 %(FWHM) at 662keV 3.4 % (FWHM) at 4.27MeV Req. for CANDLES III ; 4.0 %

7. June 5 2007 INPC20077 Radioactive BG inside CaF 2 Natural Radioactive BGs ~ Q  Maximum energy   ~ 2.6 MeV,  ~3.3 MeV,  (max)~2.7 MeVe.e. (quench; f   ~ 0.3 ) Successive decays of  in decay chain  ~1  sec decay time CaF 2 E max =5.8MeV(U) 5.3MeV(Th)  Pulse shape

8. June 5 2007 INPC20078 Development of High Purity CaF 2 Crystals Radioactivities in CaF 2 (pure) Crystal (  -ray measurement) Radioactivities in CaF 2 Powder (HPGe measurement) U-chain( 214 Bi) ~36  Bq/kg … 1/30 of Previous Crystals (14±5  Bq/kg ;Best) Th-chain( 220 Rn) ~29  Bq/kg … 1/3 of Previous Crystals ( 6±1  Bq/kg ;Best) 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 101 crystals U and Th (ICP-MS)

9. June 5 2007 INPC20079 Rejection of Double Pulse Prompt Delayed Typical Pulse Shape (500 MHz FADC) 810ns 8.8ns time(2 nsec) pulse height (ch) time(2 nsec) pulse height (ch) recorded shape fitted shape 99% of double pulse events will be rejected

10. June 5 2007 INPC200710 Pulse Shape Discrimination Pulse Shape discrimination Shape Indicator (PRC 67(2003) 014310) Difference in decay shape between  and  rays  -event  event mean value: no energy dependence (>1 MeV) 11 ~99.7% reduction at Q -value

11. June 5 2007 INPC200711 CANDLES III CANDLES III (U.G.) ‘ Sanchika ’ Kamioka CANDLES III (prototype) @Osaka University R&D

12. June 5 2007 INPC200712 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.

13. June 5 2007 INPC200713 CANDLES III (prototype) Constructed at Osaka Univ. (sea level) small version for R&D check the performance of CANDLES CaF 2 modules 10 3 cm 3 × 60 crystal; 191 kg with conversion phase Liquid scintillator  1000× h 1000 acrylic container H 2 O Buffer : passive shield   00× h 2600 PMTs 15 ” PMT (× 8) : R2018 13 ” PMT (×32) : R8055 33.4% photo-coverage 1 dirty crystal U:65 mBq/kg, Th:28 mBq/kg

14. June 5 2007 INPC200714 CANDLES III (prototype)  2.8 m h  2.6 m

15. June 5 2007 INPC200715 PMTs Photomultiplier Tube (13inch) Inside view

16. June 5 2007 INPC200716 CaF 2 module CaF 2 + conversion phase + acrylic case half filled filled Index 1.44@586nm (CaF 2 ) Index 1.46@586nm (Mineral Oil)

17. June 5 2007 INPC200717 LS tank 58 CaF 2 modules installed

18. June 5 2007 INPC200718 Conclusion Study of 48 Ca double beta decay Largest Q value CANDLES system (CaF 2 in L.S.) CANDLES III (prototype) 58 CaF 2 modules installed R&D using prototype detector at Osaka University. CANDLES III (U.G.) Design study expected BG: 0.14 events/year Construction at Kamioka will start in spring 2008

19. June 5 2007 INPC200719 Mile stone CANDLES I, II, POP CANDLES III (prototype) CaF 2 (10cm 3 ) 191 kg CANDLES III (U.G.) Kamioka underground lab. (spring 2008) CaF 2 300 kg ~30  Bq/kg for ~0.5 eV CANDLES IV 3 t; Kamioka ~3  Bq/kg for ~0.1 eV in 6 yrs CANDLES V 100 t; Kamland or ??? for ~30 meV in 7 yrs another option; enrichment