1. Recent progress of direct dark matter detection S. Moriyama Institute for Cosmic Ray Research, University of Tokyo Oct. 8 th, 2011 @ FPUA2011, Okayama, Japan

2. Principle of direct detection in Lab. Dark matter hit detectors in Lab. Why interaction expected? Assume DM particles were thermally generated. They annihilated into ordinary matter. This implies an interaction between dark matter and ordinary matter (atoms). Weakly Interacting Massive Particles (WIMPs) Dark matter Ordinary matter Annihilation Scattering 1/temperature ~ time Comoving number density

3. How much dark matter around us? It can be estimated by measuring rotational curve of the galaxy. Local density ~ 0.3GeV/cc ~average x 10 5 Isothermal, Maxwell distribution ( ~230km/s, ~10 -3 ). R.P.Olling and M.R.Merrifield MNRAS 311, 369- (2000) Buldge Steller disk Dark Halo These dark matter particles are expected to cause nuclear recoils even in underground lab.

4. Signals after nuclear recoils Small energy depositions (m p 2 /2 < 1keV), rare. Scintillation light (photons), ionizations, phonons, etc are expected to be observed. By combining multi. info., BG reduction is possible. Scintillation lights + + + + + + - - - - - - Ionization signals Phonon signals...... Bubble generation

5. Expected energy spectrum of nuclear recoil, ~O(10keV) Coherent interaction with each nucleon in nuclei causes enhancement. Target nuclei with similar mass to DM is the best choice. Si Ge Xe Si Xe Ge Red: differential, Blue: integrated R.J.Gaitskell, Ann. Rev. Part. Sci., 54 (2004) 315.

6. Another aspect: annual modulation Due to a peculiar motion of the solar system inside the galaxy, relative velocity to the rest frame of dark matter varies over a sidereal year. This causes the modulation of event rates and energy spectrum.

7. Unknown: mass and cross section! Small mass: low energy threshold detector with light nucleus ~O(GeV/c 2 ) Small cross section: massive and low BG detector ~O(1/day/ton)  3 orders/15years! Mass of dark matter particle UNKNOWN cross section to nucleon UNKNOWN True parameter Detector with larger mass, longer exposure and lower background Detector with smaller atomic number and low energy threshold

8. Experiments all over the world >30! XMASS NEWAGE PICO-LON NIT KIMS PICASSO CDMS CoGeNT COUPP DEAP/CLEAN SIMPLE DMTPC LUX DAMA/LIBRA XENON CRESSTII EDELWEISS ZEPLIN DRIFT WARP ArDM ANAIS MIMAC ROSEBUD PANDAX CDEX DM-Ice Not complete TEXONO Strong tension exists among experiments. DAMA, CoGeNT, CRESSTII  XENON, CDMS

9. 1. DAMA/NaI (7yr), DAMA/LIBRA (6yr), 430td Antonella, TAUP2011

10. Positive signal of annual modulation Radioactive pure NaI(Tl): scintillation only, no PID. Strong signature of the annual modulation, ~9  A lot of criticisms at the beginning, but later serious study/consideration started (light DM, IDM, etc.). Influences of seasonal modulating cosmic muons? An unnatural background shape is in doubt. by Sep. 2009 Modulation of +/-2%

11. 2. CoGeNT (Ge) 140kgd P-type point contact detector has very low noise thus low energy threshold due to small cap.  smaller-mass DM w/ ionization only Science 332 (2011) 1144 PRL 101, 251301 (2008) arXiV1106.0650 0

12. Assume all the unknown events from DM Mod. (  2 /dof=7.8/12) 80%C.L. accept. Flat (  2 /dof=20.3/15) 84% C.L. reject.  modulation is favored with 99.4% C.L. Is the contamination of surface background well controlled??

13. 3. XENON100, 4.8td Particle ID possible  BG red. Rafael, TAUP2011

14. Observed data and calibration 3 events remained 1.8+/-0.6BG expected (28%) Observed data Neutron source (causes nuclear recoil) calibration data 99.75% rejection line and 3 sigma contour of NR 99.75% rejection line and 3 sigma contour of NR DM search window (8.4-44.6keVnr) Nuclear recoil  e/gamma

15. Status of dark matter search DAMA, Na, 3  DAMA, I, 3  CoGeNT (Ge)90% 5-7GeV O. Buchmueller et al. CMSSM (68%, 95%) arXiv:1106.2529 Including 2010 LHC XENON100 (Xe) CRESST 2  3 orders of sensitivity improved over last 15 years! CDMS (Ge) +CDMS(LE), XENON10(LE)

16. Recent “signals” of DM, axion, and 2000: DAMA experiment (Gran Sasso) started to claim the observation of dark matter. 2005: PVLAS collaboration (INFN) axions? 2010/2011: CoGeNT (Soudan, US) 2011: CRESST II (Gran Sasso) 2011: OPERA (Gran Sasso, CERN) observation of super-luminal neutrinos

17. Recent “signals” of DM, axion, and 2000: DAMA experiment (Gran Sasso) started to claim the observation of dark matter.  >8  now 2005: PVLAS collaboration (INFN) axions?  withdrawn 2010/2011: CoGeNT (Soudan, US) 2011: CRESST II (Gran Sasso) 2011: OPERA (Gran Sasso, CERN) observation of super-luminal neutrinos “Italian signals” Further experimental check necessary

18. XMASS experiment

19. The XMASS collaborations Kamioka Observatory, ICRR, Univ. of Tokyo ： Y. Suzuki, M. Nakahata, S. Moriyama, M. Yamashita, Y. Kishimoto, Y. Koshio, A. Takeda, K. Abe, H. Sekiya, H. Ogawa, K. Kobayashi, K. Hiraide, A. Shinozaki, S. Hirano, D. Umemoto, O. Takachio, K. Hieda IPMU, University of Tokyo ： K. Martens, J.Liu Kobe University: Y. Takeuchi, K. Otsuka, K. Hosokawa, A. Murata Tokai University: K. Nishijima, D. Motoki, F. Kusaba Gifu University ： S. Tasaka 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, H. Takiya Sejong University ： Y.D. Kim KRISS: Y.H. Kim, M.K. Lee, K. B. Lee, J.S. Lee 41 collaborators, 10 institutes

20. Kamioka Observatory 1000m under a mountain = 2700m water equiv. 360m above the sea Low cosmic ray flux (10 -5 ) Horizontal access Super-K for physics and other experiments in deep underground KamLAND (Tohoku U.) By courtesy of Dr. Miyoki

21. XMASS experiment ● XMASS ◎ Xenon MASSive detector for Solar neutrino (pp/ 7 Be) ◎ Xenon neutrino MASS detector (double beta decay) ◎ Xenon detector for Weakly Interacting MASSive Particles (DM search) It was proposed that Liquid xenon was a good candidate to satisfy scalability and low background. As the first phase, an 800kg detector for a dark matter search was constructed. Y. Suzuki, hep-ph/0008296 10ton FV (24ton) 2.5m Solar, 0 , DM in future 100kg FV (800kg) 0.8m, DM First phase

22. Structure of the 800kg detector Single phase liquid Xenon (-100 o C, ~0.065MPa) scintillator – 835kg of liquid xenon, 100kg in the fiducial volume – 642 PMTs – 5keV electron equiv. (~25keV nuclear recoil ) thre.

23. BG reduction by self shielding effect Photo electric effect starts to dominate @500keV: strong self shielding effect is expected for low energy radiations. E (keV) Attenuation length (cm) water ~O(500keV) Photo Electric Effect Compton effect 10cm 1cm LXe

24. Event reconstruction

25. Demonstration of the detector performance Calibration system – Introduction of radioactive sources into the detector. – <1mm accuracy along the Z axis. – Thin wire source for some low energy  rays to avoid shadowing effect. – 57 Co, 241 Am, 109 Cd, 55 Fe, 137 Cs.. Stepping Motor Linear Motion Feed- through Top photo tube ~5m Gate valve 4mm  0.15mm  for 57 Co source Source rod with a dummy source

26. High light yield and good position resolution 57 Co source at the center shows a typical response of the detector. High p.e. yield 16.0+/-1.0p.e./keV was obtained. Factor 3 higher than expected. The photo electron yield distribution was reproduced by a simulation well. Good position res. ~1cm obtained. DATA MC [keV] Reconstructed energy 122keV 136keV 59.3keV (W-K  ) ~4% rms Data at various positions +15V

27. Expected background Major background must come from radioactivity in PMTs though we developed low BG PMTs. Radioactive impurity inside liquid xenon also must be low: 85 Kr  distillation Rn  charcoal BG ~ 10 -4 /kg/keV/day is expected to be realized. (XENON100 ~0.5x10 -4 /kg/keV/day) Background in unit mass Very low BG at low energy

28. Expected sensitivity XENON100 CDMSII XMASS 2keVee thre. 100d Black:signal+BG Red:BG Expected energy spec. 1 year exposure   p =10 -44 cm 2 50GeV WIMP Spin Independent XMASS 5keVee thre. 100d Initial target of the energy threshold was ~5keVee. Because we have factor ~3 better photoelectron yield, lower threshold = smaller mass dark matter may be looked for.

29. Assembly of PMT holder and installation of PMTs

30. Joining two halves

31. クリックしてタイトルを入力 クリックしてテキストを入力 P-01 As of Sep. 2010

32. Summary “Positive” signals by DAMA, CoGeNT, and CRESST-II (~10GeV, 10 -40 cm 2 ) are around the detector threshold where our knowledge on the detector systematic and background are not established. Further experimental confirmations are necessary, and on going. The XMASS 800kg detector aims to detect dark matter with the sensitivity 2x10 -45 cm 2 (spin independent case) with LXe. Commissioning runs are on going to confirm the detector performance and low background properties. – Energy resolution and vertex resolution were as expected. ~1cm position resolution and ~4% energy resolution for 122keV .