Ca Mo O 4 at low temperature LAAPD

Ca. Mo. O 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

Optimization of Ca. Mo. O 4 DBD Mikhrin et al. Annenkov et al. Light yield of Ca. Mo. O 4 @ LN 2 temp. increases ~ 3 times of that @ Room temperatur Can we optimize the E resolution by lowering temperature ?

LAAPD(Large Area Avalanche Photodiode) Advanced Photonics사의 16 mm 직경의 LAAPD (world largest)

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

Previous Results of LAAPD Room temperature measurements • Cs. I(Tl) + 16 mm LAAPD • 4. 8%FWHM for 662 ke. V • LAAPD has better resolution than PMT due to high Q. E. 5. 9 ke. V X-ray 9. 3% FWHM =4. 0% RMS M. Moszynski

Test Setup ORTEC PREAMPLIFIER 142 AH POWER SUPPLY( HV) Crystal (High Voltage 용 ) LAAPD Sourc e Output (Low Temperature) Output (Room Temperature) ORTEC AMPLIFIER 571 - Cs. I(Tl) & Camo. O 4(Russia) ~10 x 10 mm

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

Ca. Mo. O 4+LAAPD @Low. Temp m. V • Decay time ~ 100 ms @ -150 o. C • But shaping time of AMP is limited by 10 ms àAnalyzed Pre. Amplifier Signal directly. • Source ; Cs-137 • Temp ; -159. 2 o. C ± 0. 1 p 2 p 0 p 4 p 5 Micro sec p 6

Ca. Mo. O 4+LAAPD @-159 o. C In reality, the resolution will be worse due to poorer light collection and large size of crystal.

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 + Ca. Mo. O 4 tests down to 70 K temperature.

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

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

Quantum Efficiency of New Photocathodes Emission spectra of Ca. Mo. O 4 UBA(Ultra-bialkali), SBA(Super-bialkali), Rb. Cs(KIMS PMT), SS 25(multibialkali)

R 8520 -08 MOD Hamamatsu developed two new PMT based on R 8520 AL(XENON Group) with multialkali photocathode(SS-25) for Ca. Mo. O 4 • Size : 1” • Working temperature -200 o. C • Metal Case with Fused-Silica window.

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

Test at Sejong U. Single photoelectron spectrum @ Room temperature 750 V, X 50 Amp.

Test setup @ low temperature l Vacuum Chamber with He Cryostat can lower the temperature of crystal down to 70 K. l Ca. Mo. O 4 crystal(18 mm. X 14 mm) wrapped with Teflon sheet. - Low light yield crystal ? l SS-25 PMT attached to the crystal w/o optical grease.

Pulse shape Time (ns)

Decay time @ low temperature

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 662 ke. V peak duration. • 1. 13 photoelectrons/ke. V • w/ old crystal with low light yield. • HV not optimized at low temp. Overlapped events • Time range can be optimized.

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. • Ca. Mo. O 4 coupled with PMT under Liquid Ar should be considered.

Current KIMS PMT • Green extended ETL pmt(9269 B) • 26% @ 400 nm • 17% @ 500 nm 3” PMT (9269 QA) : Quartz window, Rb. Cs photo cathode ~5 Photo-electron/ke. V with Cs. I(Tl) crystal.

new Hamamatsu PMTS • Ultra Bialkali : – R 7600 or 3” Glass Bulb

Development of new hexagonal PMT (HAMAMATSU R 8778 MOD) for XMASS 800 kg • High quantum efficiency ~ 40% @ 175 nm • Metal package with Quartz window • Low temperature, will be immersed in Lxe.

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

Hexagonal PTFE and Co-57 source position l LED (2 mm thick PTFE filter) Distance between two PMTs : 1. 5 cm

result 122 ke. V 57 Co data 18. 9 p. e/ke. V 136 ke. V Some photons are blocked by the source itself Photoelectron statistics limit of the resolution = 2. 1%

# of photoelectrons in various LXe experiments group Lxe Mass PMT QE d. E/E # of p. e. (122 ke. V) /ke. V REF Hamamatsu R 9288(2) immersed 21% 8. 8± 0. 6% 5. 95 Ni 06 PTFE chamber 3 cm(D)X 3 cm(L) One window 2. 2 cm(D)X 7. 8 cm(L) Two window ETL 9829 QA 1 Pmts 25% 20% 0. 9± 0. 02 0. 6± 0. 02 Akimov PLB 524, 245 ZEPLIN I 5 kg ETL 9265 Q (3) 25% ZEPLIN II 31 kg 2 -phase 0 V 1 k. V/cm D 742 QKFLB 17% XENON 10 Double phase 15 kg R 8520 immersed 3. 0 ± 0. 1 DAMA 2 liter OFHC box With crystal quartz window 3 3. 5” EMI D 631/FL Thru window 0. 57 (50/88 ke. V) Bernabei 02 0. 88 ? Baldini 06 XENON UKDM MEG (PSI) 1. 5~2. 5 alner 07 16. 3% 30% coverage immersed 6% 20% 1. 1± 0. 04 0. 55± 0. 02

XENON group (at TAUP 2007) New Measurement of Scintillation Efficiency for < 10 ke. Vr • Hamamatsu R 8520 1’’× 3. 5 cm (metal channel) Xe. Cube • bialkali-PC, Quartz window, operates at -100ºC and 5 bar • Quantum efficiency > 20% @ 178 nm • Custom HV divider on Cirlex base σ/E = 7. 8 % http: //xenon. astro. columbia. edu/

Calorimetric 136 Xe DBD • Q=2467 ke. V • 208 Tl 2614. 5 ke. V Compton edge 2381. 7 ke. V • 0. 7% energy resolution(17 ke. V) @ 2467 ke. V 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.

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