1. Dark Matter Search with μTPC （ powerd by μPIC ） Micro Pattern Gas Detector 研究会 2004 年 12 月 3 日 京都大学 関谷洋之 京都大学

2. μTPC でとらえられるもの Neutral Particle ここでは、暗黒物質 neutralino についてのお話をします。 電子、 ミューオン Heavy Charged Particle フォトン X 線 ガンマ線 electron recoil Neutron proton (nuclear) recoil Neutrino electron recoil Neutralino nuclear recoil

3. 暗黒物質 2003 年 WMAP 衛星 宇宙背景放射の ゆらぎの測定 NASA/WMAP Science Team 暗黒物質（ CDM ）の量は分かったが その分布や何であるのかは依然、謎． 有力候補： SUSY に予言される neutralino の直接検出を目指した実験

4. 暗黒物質 （ニュートラリーノ） の直接検出実験 通常の物質と弾性散乱 ( 相互作用 ) することを利用 地上の検出器中の原子核の反跳を観測する 銀河ハロー中の地球の動きによる “ 風 ” 暗黒物質のシグナル 直接検出？ 太陽 DARK HALO (Maxwell 分布 ) Ｖ ０ ＝ 220km/s 暗黒物質の風 白鳥座の方向 232 km/s 京都での今日の風向き １２：００ ０：００ １８：１０

5. 反跳方向に現れる統計的 なシグナルをとらえる 散乱された暗黒物質 反跳原子核 暗黒物質の風 γ VＥVＥ μTPC による方法μ-TPC cos  CF 4 (E th =40keV) M WIMP =50GeV Drift plane N N N WIMP WIND CF 4 ガスを利用 for SD interactiong DM Track length threshold: 3 mm dE/dx threshold: 10 keV/cm μPIC の性能 Pressure [Torr] Density [g/m 3 ] dE/dx [keV/cm] 209085 低圧力での動作研究が必要

6. 10x10x10cm 3 μTPC ガス容器中 まずは Ar+C 2 H 6 中での 5.9keV X 線 Gas gain variation 1atm 0.5atm 0.2atm Ar+C 2 H 6 (9:1) Time [hour] 0.1 atm までの低圧でシグナルを確認 ガスゲインの低下は Out-Gas の影響 60cm Gas vessel  -TPC 低圧での動作試験

7. 252 Cf YAP (trigger)  -TPC low pressure gas n   p or C nuclei pressure [atm] range [mm] p 1 2.6 0.5 5.1 C 1 1.1 0.5 2.1 0.2 5.5 ２００ keV 反跳に対する 期待される range (SRIM2003) Experimental setup Ar+C2H6 gas 中性子による原子核反跳

8. n Bragg curves 3D tracking Bragg curves 計算した range 測定した range 測定した charge から のエネ ルギー が一致している 水素反跳 得られた飛跡１

9. 炭素反跳 350keV = 8mm (SRIM) n Bragg curve 得られた飛跡２

10. gas gain>7000 @ 0.25 atm で 安定動作 C,F 反跳飛跡取得の実験準備中です。 Gas gain 800600 10 4 10 3 CF 4 100% 700 Anode voltage [V] 0.25 atm0.5 atm1 atm Source: 55 Fe (5.9keV) Gas gain CF 4 100% (1atm) Ar+C 2 H 6 (1atm) Drift velocities of electrons Electric field [kV/cm] CF 4 での基礎動作試験

11. SD 3  detection sensitivities M WIMP [ GeV ]  WIMP-p [ pb ] 20042005+201? 1m 3 ×30  -TPC R&D with 800cm 3  -ray BG rejection Electron diffusion Low pressure operation n BG measurement @ Kamioka 1m 3  -TPC 実験計画 hatched ： WIMP painted ： neutron BG cos  WIMP WIND γ F F 大型化が必要 高田

13. WIMP-wind Detection with an Advanced Gaseous Tracking Device Atsushi Takeda T. Tanimori, H. Kubo, K. Miuchi, T. Nagayoshi, H. Sekiya, R. Orito, A. Takada, Y. Okada, H. Nishimura, K. Hattori Kyoto University DARK2004 6 October, 2004 Texas A&M University, College Station, TX, USA

14. Table of Contents 1. Direction sensitive WIMP search 2.  -TPC: 3-D tracking device 3. WIMP-wind detection with  -TPC 4. Study with 10cm-size detector as a WIMP-wind detector 5. Summary

15. 1. Direction sensitive WIMP search Recoil energy [keV] [counts/keV/day/kg] Only a few % rate difference Detecting only energy spectra with a conventional detector  WIMP-wind is blowing from the direction of the Solar motion Drift plane μ-TPC N N N WIMP WIND γ F F Detecting WIMP-wind distribution with a gaseous tracking device cos  CF 4 (E th =40keV), M WIMP =50GeV Very large asymmetry WIMP WIND

16. Cathode Anode 400  m 100  m 50  m Drift plane electron cloud  2-D imaging detector  400  m pitch electrodes  simple structure  stable operation  large area (PCB technology) μ μ-PIC + TPC (x, y)(drift time)  -PIC 2.  -TPC: advanced gaseous device 3D tracking μ μ-TPC: with a micro pixel chamber (  -PIC) readout

17.  -PIC, Micro Pixel Chamber Cathode Anode 10cm  Practical size (10cx10cm 2 )  -PICs are working well  Now, large size (30x30cm 2 )  -PIC is being manufactured 30cm

18. Gas gain 440600520 Anode voltage [V] 10 4 10 3 Ar:C 2 H 6 = 8:2 Ar:C 2 H 6 = 9:1 (gas gain ~6000)  High gas gain max: 16000  Good gain uniformity ~4.5% (  )  Good spatial resolution ~120  m (  )  Stable operation >1000 hours 10cm Gain uniformity Performance of the 10x10cm 2  -PIC (1/2) Anode [cm] Cathode [cm] NIM A 525 (2004) 20

19. Performance of the 10x10cm 2  -PIC (2/2) FWHM 30% MnK  Ar-esc 5.9keV 55 Fe spectrum @ 10cmx10cm ADC [ch] 0.5mm slits Xe:C 2 H 6 = 7:3 Length along the edge [mm] Counts Knife edge test position resolution σ=120  m X-ray image 1mm

20. Prototype  -TPC  10×10×10cm 3 detection volume E=500V/cm 10cm 0.2mm Cu wires

21. Encoder board ASD board  -TPC VME Memory Board 512ch summed analog (8ch) 512ch LVDS digital 32bit DAQ system VME FADC 100MHz 8ch 256ch (anode) 256ch (cathode) 256ch (anode) 256ch (cathode) 3-D tracking Bragg curves  Amplifier-Shaper- Discriminator (ASD) chip  5 FPGAs  take anode-cathode coincidence @ 50MHz

22. Performance of the  -TPC (1/2) Proton tracks electron tracks  3-D tracks obtained with Ar+C 2 H 6 of 1atm n 252 Cf

23. Performance of the  -TPC (2/2)  Gamma-ray rejection NIM A517 (2004) 219 nucleus event dE/dX [keV/cm] 22 Na (γ)  2 /d.o.f. dE/dX [keV/cm] χ 2 /d.o.f 252 Cf (n+γ)  2 /d.o.f. 0 10 20 30 100200300400500 χ 2 /d.o.f 0 30 20 10 100200300400500 (511keV  ) Nucleus events have large dE/dx straight track

24. 3. WIMP-wind detection with  -TPC  Comparing to the other experiment Our  -TPC DRIFT project  Fine pitch (400  m)  3-D tracking  Mechanically stable  Mass production (PCB technique)  First detector with sensitivity to the directions of nuclear recoils  MWPC with 2mm pitch  2-D tracking only wireless, no 3-D geometry

25. as of shown in PLB 578 (2004) 241  Experimental parameters used for the calculation Detection sensitivities Target gas: CF 4 for Spin-dependent (SD) interaction Track length threshold: 3 mm dE/dx threshold: 10 keV/cm  -ray discrimination ~100% Bragg curves are detected gasPressure [Torr] Density [g/m 3 ] dE/dx [keV/cm] CF 4 209085 Need to study low-pressure  -TPC

26. Expected WIMP signal WIMP WIND γ F F hatched ： WIMP painted ： neutron BG cos  @Kamioka  CF4 20Torr  Fast neutrons are the only BG source  50cm water shield  Forward/Backward asymmetry

27. Detection sensitivities Spin-dependent M WIMP [ GeV ]  WIMP-p [ pb ]  Estimated 3  detection sensitivities at Kamioka Observatory for SD interaction

28. 4. Study with 10cm-size detector as a WIMP-wind detector  Operation with low-pressure gas  3-D tracking with low-pressure Ar+C 2 H 6 gas  Operation with CF 4 gas including 19 F whose large cross section for SD interaction Required operation pressure: 0.05 ~ 0.2 atm Confirm tracking capabilities under low-pressure using a standard gas Properties of CF 4 gas

29. Operation with low-pressure gas  10x10x10cm 3  -TPC in the gas vessel  Gas vessel is available for 30x30 cm 2 detector 60cm Gas vessel Gas gain variation 1atm 0.5atm 0.2atm Ar+C 2 H 6 (9:1) Time [hour]  Signals were observed down to 0.1 atm  Out-gas should be suppressed  -TPC

30. 252 Cf YAP (trigger)  -TPC low pressure gas n   p or C nuclei pressure [atm] range [mm] p 1 2.6 0.5 5.1 C 1 1.1 0.5 2.1 0.2 5.5 Calculated range of nuclei whose energy of 200 keV (SRIM2003) 3-D tracking with low-pressure Ar+C 2 H 6 gas  Experimental setup

31. Obtained 3-D tracks (1/2) n Bragg curves  3D tracking  Bragg curves range v.s. charge roughly agrees with SRIM  tracks of recoil protons

32.  Carbon candidate 350keV = 8mm (SRIM) n Obtained 3-D tracks (2/2) Bragg curve

33.  Stable operation with gas gain>7000 @ 0.25 atm  Confirmed drift velocities of electrons in CF 4 gas are fast Gas gain 800600 10 4 10 3 CF 4 100% 700 Anode voltage [V] 0.25 atm0.5 atm1 atm Source: 55 Fe (5.9keV) Gas gain CF 4 100% (1atm) Ar+C 2 H 6 (1atm) Drift velocities of electrons Electric field [kV/cm] Operation with CF 4 gas

34. 4. Summary  WIMP-wind detection   -PIC has a fine pitch (400  m)  Study with 10cm-size detector  Low pressure operation (0.2 atm)  Proton and carbon 3-D tracks  Properties of CF 4 gas  30cm-size TPC will be ready at the end of 2004

37. Organic scintillators - Minowa group (Tokyo) Gas detectors - DRIFT （ UK ） -  -TPC （ Kyoto ）  -PIC with 400  m pitch  -PIC with 400  m pitch 3-D tracking 3-D tracking Mechanically stable Mechanically stable UKDMC, Occidental College, Temple Univ., LLNL First detector with sensitivity to First detector with sensitivity to the directions of nuclear recoils the directions of nuclear recoils MWPC with 2mm pitch MWPC with 2mm pitch 2-D tracking only 2-D tracking only DRIFT project Our  -TPC wireless, no 3-D geometry Mass production Mass production Direction sensitive detector under development  n Anode [cm] Drift [cm] Cathode [cm]

38. Time schedule SD 3  detection sensitivities M WIMP [ GeV ]  WIMP-p [ pb ] SI 3  detection sensitivities M WIMP [ GeV ]  WIMP-n [ pb ] 20042005+201? 1m 3 ×30  -TPC R&D with 800cm 3  -TPC  -ray BG rejection Electron diffusion Low pressure operation “Detection” by Forward/Backward 3σasymmetry n BG measurement @ Kamioka 1m 3  -TPC

39. track direction is important track only track+direction F/B ~ 5 F/B ~ 1.3

40. Expected rate –threshold: 40keV –WIMP mass: 50 GeV for F, Ar 100GeV for Xe –WIMP- ｐ cross section : 0.1 pb for SD 10 -6 pb for SI gaspressure [torr] density [g/m 3 ] rate [cpd/kg] Event (10m 3 ×1yr) CF 4 20900.21260 Ar20470.0344.1 Xe(SD)5100.0111.4 Xe (SI)5380.0799.6

41. S/N calculation –threshold: 40keV –WIMP mass: 50 GeV for F, Ar 100GeV for Xe –WIMP- ｐ cross section : 0.1 pb for SD 10 -6 pb for SI gasEvent (30m 3 ×3yr) F/B ratio Modulation (σ) n BG ×1/100 CF 4 23401420σ40σ Ar37110.4σ3σ Xe(SD)1350.1σ1σ Xe (SI)8650.4σ5σ

42. Expected 95 % C.L. sensitivities Spin-DependentSpin-Independent Xe 30 m 3, 3 years 35cm water shield Xe 10 m 3, 1 year noshield CF 4 10 m 3, 1 year noshield CF 4 30 m 3, 3 years 35cm water shield

43. spectrum Threshold dependency of F/B gas: CF 4 WIMP-p: 0.1 pb forward/backward increases with the increases with the threshold energy threshold energy