方向感度をもつ暗黒物質検出器の開発をめざした 異方性を有するシンチレータ開発の検討 黒澤俊介 A, B, 関谷洋之 C, 村上力輝斗 A, 庄子育宏 A, 大橋雄二 A, 鎌田圭 B, 横田有為 B, 吉川彰 A, B 東北大金研 A, 東北大 NICHe B, 東大宇宙線研 C 2015 年 9 月 28 日 大阪市立大学 日本物理学会 2015 年秋季大会 28aSJ-10 This work is supported by JSPS KAKENHI Grant Number 15K13478 (Started from Apr. 2015) Total 17 pages!

2 日本物理学会 2015 年秋季大会 大阪市立大学 28aSJ-10 Directional response with MeV alpha particles DAMA’s report “Estimated” quenching 5keV ~30% difference 40~50% difference

3 日本物理学会 2015 年秋季大会 大阪市立大学 28aSJ-10 θ P.H. Heckmann et al.,Z. Phys. 162 (1961) % difference Only 7% HS et al., Physics Letters B 571 (2003) 132 Directional response with MeV alpha particles Measured quenching only 7 % difference In case of stilbene crystal

4 日本物理学会 2015 年秋季大会 大阪市立大学 28aSJ-10 Directional detectors must aim at < cm 2 To go beyond the NC- wall arXiv: J.Billard et al.

5 日本物理学会 2015 年秋季大会 大阪市立大学 28aSJ-10 How much ZnOW 4 is necessary in Kamioka? Although “direction” is not detected directly… it’s a direction-sensitive detector

6 日本物理学会 2015 年秋季大会 大阪市立大学 28aSJ-10 Assuming 7% Including atmospheric & DSNB BG 10 tons x 1000 days exposure! Expected “diurnal modulation” c axis // North-South c axis // East-West c.f. Proton decay 22.5 ktons x 6000 days

7 日本物理学会 2015 年秋季大会 大阪市立大学 28aSJ-10 2 x 2 x 2 mm 3 crystal made by Czochralski process Started to prepare (10 tons of) ZnWO 4 ! 2.0 mm 0.2 mm 2.0 mm At Tohoku University A 2mm cubic crystal was cut and polished. To discern the direction of the crystal

8 日本物理学会 2015 年秋季大会 大阪市立大学 28aSJ-10 Monoclinic crystal system Crystal structure of ZnWO 4 Schofield et al., Acta Crystallographica, Section B: Structural Science (1997) 53, p102-p112 a [Å]b[Å]c[Å] α [deg]β [deg]γ [deg] Lattice type P Space group name P 2/c Space group number 13 Setting number 1 Almost cubic!

9 日本物理学会 2015 年秋季大会 大阪市立大学 28aSJ-10 X-ray irradiated from each axes of ZnWO 4 Simulated Laue patterns c-axisb-axisa-axis

10 日本物理学会 2015 年秋季大会 大阪市立大学 28aSJ-10 X-ray generator: RIGAKU RAD-IIC with Hamamatsu CCD –25kV, 30mA, Target ： Cu –exposure ： 240ns Distance between CCD and ZnWO 4 :4cm Actual Laue pattern X-rays c-axis This plane is really perpendicular to c-axis!

11 日本物理学会 2015 年秋季大会 大阪市立大学 28aSJ-10 Actual Laue patterns X-rays b-axisa-axis ~b axis ~a axis

12 日本物理学会 2015 年秋季大会 大阪市立大学 28aSJ-10 Hamamtsu R7600U-200 UBA PMT –QE For fixed crystal position, Teflon + Al mounter were attached to the PMT Setup with PMT Photocathode Reflector/mounter ZnWO 4 10 mm R7600U Am Paper Black tape ZnWO 4 optical grease Oken 6262A

13 日本物理学会 2015 年秋季大会 大阪市立大学 28aSJ-10 From ~a axis direction, “attach – remove – attach” cycled Both 59.5keV peak and 5.5MeV positions are same. Reproducibility check keV X-ray 5.5MeV  Temperature o C

14 日本物理学会 2015 年秋季大会 大阪市立大学 28aSJ-10 From ~a axis direction, but the other side of the crystal Both 59.5keV peak and 5.5MeV positions are same. Reproducibility check keV X-ray 5.5MeV  Temperature o C

15 日本物理学会 2015 年秋季大会 大阪市立大学 28aSJ-10 From ~a axis direction, ~b axis direction, and c axis direction ~12% difference in 5.5MeV  peaks, while 59.5keV peaks are same. Main result 59.5keV X-ray 5.5MeV  Temperature o C ~a axis ~b axis c axis

Directional response of ZnWO 4 was confirmed. –12%  with sys. error –Surface lattice defect affects? More perfect crystal has smaller directional response? Summary 16 日本物理学会 2015 年秋季大会 大阪市立大学 28aSJ-10 To Do Evaluation with another samples of the crystal Intrinsic background checks Neutron beam test Prepare 10 tons of ZnOW 4

17 日本物理学会 2015 年秋季大会 大阪市立大学 28aSJ-10 At research lab. on advanced crystal engineering, IMR, Tohoku University For larger crystals Many Czochralski machines for 3inch-size crystal. –~ 10kg x 1000 = 10 tons? –It takes 2 weeks to make one. Optimization for ZnWO 4 is underway.

Extra Slides 18 日本物理学会 2015 年秋季大会 大阪市立大学 28aSJ-10

Scintillation wavelength was measure with 241 Am (5.5MeV  ) –Spectrometer: Edinburgh Instrument FLS920 Scintillation wavelength 19 Hiroyuki Sekiya CYGNUS2015 Occidental College June c.f. Grabmaier IEEE TNS 31 (1984 ) 372 Scintillation mechanism –Charge transfer emission Peak –There is a reproducible sharp structure around 450nm –Under investigation

Decay constant :10  sec Scintillation waveform 20 Hiroyuki Sekiya CYGNUS2015 Occidental College June Oscilloscope Tektronix TDS 3034B Fitted function f = A 1 exp(-t/τ 1 ) + C τ 1 : 10 μsec References Grabmaier IEEE TNS 31 (1984 ) 372 –21.8  s Holl et al., IEEE TNS 35, (1988) 105 –20.0  s Shkulkova et al., IEEE TNS 56 (2009) 994 –700 ns & 7,000 ns & 25,000 ns Depends on each crystal? –Lattice Defect affects? –Temperature dependence? –Will be investigated

Will be tested with FADC Setup for spectral measurement 21 Hiroyuki Sekiya CYGNUS2015 Occidental College June MCA AMPTEK8000A preamp ORTEC 113 C=1000pF shaper ORTEC 572A Shaping time: 10  sec

Scintillation wavelength: peak ~480nm Scintillation decay time: ~10  s –There are differences between previous studies. –Lattice defect affects? –Light yield must be checked. Directional response was confirmed. –12%  with sys. error –Lattice defect affects? More perfect crystal has smaller directional response? Summary of what we did so far 22 Hiroyuki Sekiya CYGNUS2015 Occidental College June

Evaluation with another samples of the crystal Light yields check with gamma rays. –23% of NaI Holl et al., IEEE TNS 35, (1988) 105 Intrinsic background checks Temperature dependence of LY. – F. Cappella et al., Eur. Phys. J. C (2013) 73:2276 –Directional respose remains? Neutron beam test Prepare 10 tons of ZnOW 4 To do 23 Hiroyuki Sekiya CYGNUS2015 Occidental College June

At research lab. on advanced crystal engineering, IMR, Tohoku University For larger crystals 24 Hiroyuki Sekiya CYGNUS2015 Occidental College June Many Czochralski machines that can make 3inch-size crystal. –~ 10kg x 1000 = 10 tons? –It takes 2 weeks to make one. Optimization for ZnWO 4 is underway.

In Japan, a consortium for low BG techniques was organized by KAKENHI budget (Grants-in-Aid for Scientific Research, MEXT) ~15M$ for 5 years With PICO-LON and CANDLES –Low BG crystal technologies are being developed. For Low BG crystal 25 Hiroyuki Sekiya CYGNUS2015 Occidental College June