1. CaMoO 4 at low temperature - LAAPD and PMTs - Woonku Kang, Jungil Lee, Eunju Jeon, Kyungju Ma, Yeongduk Kim Sejong University for KIMS collaboration Double Beta Decay workshop 2009. 10. 16

2. Optimization of CaMoO 4 DBD Annenkov et al.Mikhrin et al. Light yield of CaMoO4 @ LN2 temp. increases ~ 3 times of that @ Room temperature.  Can we optimize the E resolution by lowering temperature ?

3. LAAPD ( Large Area Avalanche Photodiode ) Advanced Photonics 사의 16mm 직경의 LAAPD (world largest)

4. High quantum efficiency : ~ 90% @ 500nm High quantum efficiency : ~ 90% @ 500nm Solovov(1999) 5mm LAAPD Can operate at low temperature Significantly reduced dark current Higher gains can be achieved Noise level can be reduced CaMoO4 + LAAPD can be excellent detector for DBD

5. Previous Results of LAAPD CsI(Tl) + 16mm LAAPD 4.8%FWHM for 662 keV LAAPD has better resolution than PMT due to high Q.E. M. Moszynski Room temperature measurements 5.9 keV X-ray 9.3% FWHM =4.0% RMS

6. Test Setup Source ORTEC PREAMPLIFIER 142AH (High Voltage 용 ) POWER SUPPLY( HV) ORTEC AMPLIFIER 571 Crystal LAAPD Output (Room Temperature) Output (Low Temperature) - CsI(Tl) & CamoO4(Russia) x10x10mm ~10x10x10mm

7. CsI(Tl)+LAAPD @Room temperature Compton edge Channel number # of events Back scatters (6%FWHM) We confirmed good resolution of CsII(Tl)+LAAPD detector at room temperature

8. CaMoO 4 +LAAPD @LowTemp Decay time ~ 100  s @ -150 o C But shaping time of AMP is limited by 10  s  Analyzed PreAmplifier Signal directly. Source ; Cs-137 Temp ; -159.2 o C ± 0.1 Micro sec mV p4p4 p6p6 p0p0 p2p2 p5p5

9. In reality, the resolution will be worse due to poorer light collection and large size of crystal. CaMoO4+LAAPD @-159 o C

10. Future plan Try to understand the cause of LAAPD failure, specially for the dye sensor. New cryostat and vacuum chamber for LAAPD and new PMT + CaMoO4 tests down to 70K temperature.

11. New PMTs of Hamamatsu - first talk with company in 2007-

12. Requirements to Hamamatsu on New PMTs for DBD experiment High QE in 520 nm region. –SBA or UBA photocathode Low radioactive background –prefer Quartz window+Metal package Size of Photocathode –1” ~ 2” circular or square Low temperature operation –Upto -200 degree is desired

13. Quantum Efficiency of New Photocathodes Emission spectra of CaMoO 4 UBA(Ultra-bialkali), SBA(Super-bialkali), RbCs(KIMS PMT), SS25(multibialkali)

14. Hamamatsu developed two new PMT based on R8520AL(XENON Group) with multialkali photocathode(SS-25) for CaMoO 4 Size : 1” Working temperature -200 o C Metal Case with Fused-Silica window. R8520-08MOD

15. Low temperature test by Hamamatsu Hamamatsu tested the linearity of cathode sensitivity (~ Quantum efficiency) down to -165 degree.  < 1% effect.

16. Test at Sejong U. Single photoelectron spectrum @ Room temperature 750V, X50 Amp.

17. Test setup @ low temperature Vacuum Chamber with He Cryostat can lower the temperature of crystal down to 70K. CaMoO4 crystal(18mmX18mmX14mm) wrapped with Teflon sheet. - Low light yield crystal ? SS-25 PMT attached to the crystal w/o optical grease.

18. Time (ns) Pulse shape

19. Decay time @ low temperature

20. Single photoelectron spectrum worse resolution than @ room temperature Number of photoelectron distribution. Due to long decay time, many events are ovelapped in 300 micro second time duration. 1.13 photoelectrons/keV w/ old crystal with low light yield. HV not optimized at low temp. Time range can be optimized. 662 keV peak Overlapped events

21. Summary LAAPD is an excellent photo sensor. However, the stable operation at low temperature should be confirmed. Low temperature PMT with high QE & low background is under development. CaMoO4 coupled with PMT under Liquid Ar should be considered.

24. Current KIMS PMT Green extended ETL pmt(9269B) 26% @ 400nm 17% @ 500nm 3” PMT (9269QA) : Quartz window, RbCs photo cathode ~5 Photo-electron/keV with CsI(Tl) crystal.

25. new Hamamatsu PMTS Ultra Bialkali : –R7600 or 3” Glass Bulb

26. Development of new hexagonal PMT (HAMAMATSU R8778MOD) for XMASS 800 kg High quantum efficiency ~ 40% @ 175 nm Metal package with Quartz window Low temperature, will be immersed in Lxe.

27. Inside of the chamber Top PMT Bottom PMT Test chamber Hexagonal PTFE

28. LED (2mm thick PTFE filter) Hexagonal PTFE and Co-57 source position Distance between two PMTs : 1.5cm

29. 18.9 p.e/keV 122keV 57 Co data 136keV Some photons are blocked by the source itself result Photoelectron statistics limit of the resolution = 2.1%

30. # of photoelectrons in various LXe experiments groupLxe Mass PMTQEdE/E (122keV) # of p.e. /keV REF XENONHamamatsu R9288(2) immersed 21%8.8±0.6%5.95Ni06 UKDMPTFE chamber 3cm(D)X3cm(L) One window 2.2cm(D)X7.8cm(L) Two window ETL 9829QA 1 Pmts 2 Pmts 25%20% 0.9±0.02 0.6±0.02 Akimov PLB524, 245 ZEPLIN I5kgETL 9265Q (3) 25%1.5~2.5 ZEPLIN II31kg 2-phase 0V 1kV/cm D742QKFLB17% 16.3%1.1±0.04 0.55±0.02 alner07 XENON 10 Double phase 15kg R8520 immersed 3.0 ± 0.1 DAMA2 liter OFHC box With crystal quartz window 3 3.5” EMI D631/FL Thru window 0.57 (50/88 keV) Bernabei02 MEG (PSI) 30% coverage immersed 6% 20% 0.88 ? Baldini06

31. XENON group (at TAUP 2007) New Measurement of Scintillation Efficiency for < 10 keVr XeCube Hamamatsu R8520 1’’×3.5 cm (metal channel) bialkali-PC, Quartz window,operates at -100ºC and 5 bar Quantum efficiency > 20% @ 178 nm Custom HV divider on Cirlex base http://xenon.astro.columbia.edu/ σ/E = 7.8 %

32. Calorimetric 136 Xe DBD Q=2467 keV 208 Tl 2614.5 keV Compton edge 2381.7 keV 0.7% energy resolution(17keV) @ 2467keV expected.  DBD peak and Compton edge separation is ~5 sigma. Maybe worth to study in detail, specially for events between full peak and Compton edge for a specific detector geometry and shielding. Both single & double phase can be tried.

33. Summary LAAPD has (dis)advantage. New PMTs will improve the sensitivities of DBD and DM experiments. Constant optimization is important.