The XMASS experiment

Transcription

1 The XMASS experiment

2 The XMASS Collaboration Kamioka Observatory, ICRR, Univ. of Tokyo: Y. Suzuki, M. Nakahata, S. Moriyama, M. Yamashita, Y. Koshio, A. Takeda, K. Abe, H. Sekiya, H. Ogawa, K. Kobayashi, K. Hiraide, K. Ueshima, A. Shinozaki, H. Nishiie, S. Hirano IPMU, University of Tokyo: K. Martens, J.Liu Kobe University: Y. Takeuchi, K. Otsuka Saga University: H. Ohsumi Tokai University: K. Nishijima, D. Motoki Gifu University: S. Tasaka Waseda University: S. Suzuki Yokohama National University: S. Nakamura, I. Murayama, K. Fujii Miyagi University of Education: Y. Fukuda STEL, Nagoya University: Y. Itow, K. Masuda, H. Uchida, Y. Nishitani Seoul National University: S.B. Kim Sejong University: Y.D. Kim KRISS: Y.H. Kim, M.K. Lee, K. B. Lee, J.S. Lee

3 What s XMASS 1. XMASS experiment Multi purpose low-background experiment with liq. Xe Y. Suzuki et al., hep-ph/ Xenon MASSive detector for solar neutrino (pp/ 7 Be) Xenon neutrino MASS detector (ββ decay) Xenon detector for Weakly Interacting MASSive Particles (DM search) Solar neutrino Dark matter Double beta As a 1 st phase, an 800kg detector for dark matter search is under construction. 3

4 800kg detector Water tank Elec. hut Refrigerator Inner and Outer OFHC copper vessel 11m 857kg xenon 10m 72 20inch PMTs (veto) ~ 1.2m 642 PMTs

5 Structure of the 800kg detector Single phase liquid Xenon detector 857kg of liquid xenon, 100kg in the fiducial volume 642 PMTs (630 hex +12 round) Q.E. : 28-39% Photo coverage: 62.4% 3D event reconstruction 5keVee threshold with 4.4pe/keVee 58.4 Hex: R Round: R MOD 310mm Φ1113mm Φ

6 Expected sensitivity Spin Independent Case XENON10 CDMSII σ χp >2x10 45 cm 2 for GeV WIMP, 90%C.L. 1yr exposure, 100kg FV, BG: 1x10 4 /kev/d/kg Scintillation efficiency: 0.2 XMASS 1yr Expected energy spectrum 1 year exposure σ χp =10-44 cm 2 50GeV WIMP Black:signal+BG Red:BG

7 2. Background reduction (1) BG from detector materials 642 PMTs: Main BG source although RI level is 1/100 of ordinary PMT. OFHC copper: Bring in the mine < 1month after electrorefining (Mitsubishi Material Co.) Other materials: All the components were selected with HPGe and ICP-MS. (>250 samples were measured) The total RI level is much lower than PMT BG. We developed new ultra low RI PMT with Hamamatsu. (1/100 of ordinary one).

8 Self-shielding for BG from PMTs BG/PMT [mbq] U chain / Th chain / K < Co / PMT PMT Counts/day/kg/keV kev γ tracking < 10-4 /kev/day/kg (100kg F.V.) Counts/day/kg/keV n contribution < 2.2x10-5 /d/kg kev

9 (2) External BG (γ, n) from rock γ and n from rock are sufficiently reduced by a 2m thickness pure water tank: γ < γ from PMT, n << 10-4 /day/kg 10m dia. and 11m height water tank for future extensions PMTs for active veto for CR μ. 11m 10m Reduction of gamma rays γ PMT BG level 2m needed Att. vs. thickness (m) y [cm] 10 7 n s water Liq. Xe n X [cm] 5m dia. = ~2m wall thickness

10 (3) Internal BG (1) : Kr Kr ( 85 Kr: Q β =687keV, τ=10.8y) can be reduced by distillation. Our goal: Kr < 1ppt ( <10-5 /day/kev/kg) 5 order of magnitude reduction with 4.7kg/hr processing time was achieved. K. Abe et al. for XMASS collab., Astropart. Phys. 31 (2009) 290 Target value can be achieved Distillation tower in 10 days for 1ton xenon. (0.1ppm 1ppt) commercial LXe intake GKr outlet 4m Xe Boiling point (@0.2MPa) 178 K Kr LXe outlet Kr 140~150 K

11 (4) Internal BG (2) : Rn Measured Rn emanation rate from all materials is < 15mBq Our goal: 222 Rn < 0.6 mbq/ton (<10-5 /kev/day/kg) Continuous Rn removal with xenon circulation is needed. Filtering: by gas and liquid. Under study. Charcoal Filter GXe <30 liter GXe/m LXe ~a few liter LXe/m

12 Each components and construction status Calibration system Electronics hut LXe tank Distillation Tower GXe buffer tank 10m3 x 2, <10bar Clean booth at the entrance GXe compressor Experimental hall, water shield, and gas handling syst.

13 The PMT holder: construction Nov m 4.0 m 3.0 m

14 The PMT holder: PMT installation 642 PMTs are attached during 13 days. 200g/PMT ~200kg for all PMTs

15 The PMT holder: PMT installation All PMTs attached, except boundary 30. Boundary 30 PMTs were attached after connection of upper and lower half.

16 The PMT holder: Connection of two halves

17 The PMT holder: Fillter attachment. Total 2.8ton: end of Feb. 2010

18 Manufacturing detector vessel A challenge: Manufacturing a large flange with soft OFHC copper. Inside: Electropolished Due to insufficient strength of its neck part, it needed to be reinforced by adding ribs. It took four months.

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20 Inner vessel chamber

21 Outer vessel chamber

22 Circulation system Gas circulation <30L/min gas pump Cable line Calibration line filters emergency gas pump 100L/min XMASS circulation system Gas phase: < 30 L/min Liquid phase: ~ 5 L/min 857kg Water tank Outer vacuum Condenser 360W evaporator liquid pump Liquid circulation ~5L/min filters 700L Liq. Storage 10 m 3 x 2 gas storage

23 700 L Liquid xenon reservoir 10m 3 emergency reservoir and compressor. Compressor 700L can be contained. Collect xenon with liquid and keep. Vacuum insulation PTR degree Liquid nitrogen line. In the case of emergency we can collect xenon gas by compressor. 1ton, 170m3 xenon gas with 9MPa. 100 L/min flow rate.

24 857kg Outer vacuum Liquid pump Max Condenser 5L/min 2 PTR 180W@- 100degree x2 Estimated heat invasion to the detector is ~50W. Liquid nitrogen line is also equipped. Gas circulation <30L/min gas Cable line pump Calibration filters Water tank line evaporato Condenser r 360W filters liquid pump Liquid circulation emergency gas pump 100L/min 700L Liq. Storage 10 m 3 x 2 gas storage

25 Gas pump Max 30L/min Gas circulation <30L/min gas pump Cable line Calibration line filters Gas filter To remove Rn, use charcoal PTR Evaporator To keep Max 30L/min gas flow. emergency gas pump 100L/min 857kg Water tank Outer vacuum evaporator Condenser 360W filters liquid pump Liquid circulation ~5L/min 700L Liq. Storage 10 m 3 x 2 gas storage

26 Calibration system Gamma source To check Position reconstruction Energy resolution From inside and outside of the detector. LED PMT Gain (1pe) 8 LEDs are attached to the PMT holder. Laser + diffuser PMT Timing

27 Linear drive + stepping moter Linear and rotary drive source Calibration system for inside detector To introduce calibration source to inside detector Operate from the water tank top, 5m above detector Liquid xenon ~5m Gate valve Move top PMT and make window through which source can enter Introduce source to inside of the detector. Open/close of the window can be checked by optical fiber scope. Top PMT Inside of detector Source can be changed even during observation. 27

28 PMT drive system Tank top (atmosphere) Linear and rotary drive Constant force spring handle Control rod Lift up 150mm Rotate 90 degree Inside detector (xenon) Top PMT 28

29 Calibration source rod φ12mm, length 1560mm,1.54kg Lift up and down by φ0.3mm SUS301 wire Calibration source is attached at the end of rod. Source +holder (exchangable) Adaptor (SUS304) OFHC 29

30 3. Prepared source nuclide energy [kev] strength [Hz] diameter [mm] package material (1) Fe brass (2) Cd , 25, brass (3) Am SUS (4) Co SUS (1) Fe-55 and (2) Cd-109 are sealed in 50μm thickness brass tube Pressurized test (1MPa) Leak check at low temperature. Fe φ5mm 50mm 30

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32 4.Schedule in near future 9 月 10 月 11 月 Distillation to get rid of Kr Circulation line construction 20 PMT Installation in water tank. Introduce liquid xenon, circulation and purification Calibration Check detector response and xenon quality Start observation Distillation and installation of 20 PMT have been finished. Observation will start after confirmation of xenon quality and detector performance by calibration.

33 Summary XMASS 800kg detector Use 1ton liquid xenon. Single phase detector. Target sensitivity 10-45cm2 BG level 10-4/keV/kg/day Background From detector, material selection and self shielding. External gamma and neutron, water shield. Internal, Kr and Rn, distillation and purification. Construction Most parts finished. PMT holder, IVC, OVC. Schedule Distillation and installation of 20 PMTs finished. Finishing circulation line. Introduction of liquid xenon and calibration will be start soon. After confirmation of detector performance, observation will start.

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35 較正装置の設置 ( 水タンク上 ) ステッピングモータ 巻取りドラム ワイヤー (SUS301, 直径 0.3mm) 較正源棒 ( 無酸素銅 直径 12mm, 長さ 1560mm) 3m 較正源交換窓 ゲートバルブ ( 内径 40mm) 水タンク上 PMT 操作ハンドル 較正用配管

36 較正装置の設置 ( 検出器内 ) 較正源棒ガイドパイプ 検出器内 着座センサー PMT ホルダー 較正源棒 ( 検出器最下部位置 ) 36

37 Rn removal test in gas circulation Charcoal housing Charcoal whose suitable hole size (~10A ) was selected. Tested in -105, with 10Bq Rn in xenon. More than 85% Rn removal was achieved. (charcoal weight: 25g, trap length: 60cm, flow rate: 0.5L/min). Rn removal efficiency is now being improved with more suitable trap length and flow rate. In the case of Rn removal emanated from only gas phase, our goal (<0.6mBq) can be achieved with 1.0 L/mim flow rate. Rn removal emanated from liquid phase is now under study.

38 4. スケジュール 月 検出器の状態 較正 9 上旬 検出器のタンク内設置完了 レーザーによるタイミング測定 ( 終了済 ) タンク外配管作業 10 中旬 下旬 上旬 中旬 下旬 検出器真空引き ベーキングタンク内 veto PMT 取付キセノン蒸留 (1ton) 検出器真空引き ベーキングタンク水はり試験 (PMT 取付 ) 検出器冷却 キセノン導入 (getter, evaporator) データ取得いったん回収その後 再度導入 (getter, evaporator) OD PMT 較正 ( シンチレータボール ) 外部 内部 γ 較正源を使って光量測定 キセノンの quality check 内部 γ 較正源を使ってパラメータ ( 吸収 散乱長等 ) tuning 外部 γ 源を使って wall effect study 11 長期データ取得 パラメータ tuning 内部 LED 外部 γ 源による daily calib. 検出器安定性を常にモニタ