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Recent progress of direct dark matter detection

Recent progress of direct dark matter detection. S. Moriyama Institute for Cosmic Ray Research, University of Tokyo Oct. 8 th , 2011 @ FPUA2011, Okayama, Japan. Principle of direct detection in Lab. Dark matter hit detectors in Lab. Why interaction expected?

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Recent progress of direct dark matter detection

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  1. Recent progress of direct dark matter detection S. Moriyama Institute for Cosmic Ray Research, University of Tokyo Oct. 8th, 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 Comoving number density Scattering Dark matter Ordinary matter Annihilation 1/temperature ~ time

  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 105 • Isothermal, Maxwell distribution (<v> ~230km/s, <b>~10-3). R.P.Olling and M.R.Merrifield MNRAS 311, 369- (2000) • These dark matter particles are expected to cause nuclear recoils even in underground lab. Dark Halo Steller disk Buldge

  4. Signals after nuclear recoils • Small energy depositions (mp <v>2/2 < 1keV), rare. • Scintillation light (photons), ionizations, phonons, etc are expected to be observed. • By combining multi. info., BG reduction is possible. - - - + + + Ionization signals Scintillation lights ...... 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. Ge Xe Xe Si Ge Si 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! cross section to nucleon UNKNOWN • Small mass: low energy threshold detector with light nucleus ~O(GeV/c2) • Small cross section: massive and low BG detector ~O(1/day/ton)  3 orders/15years! Detector with smaller atomic number and low energy threshold Detector with larger mass, longer exposure and lower background Mass of dark matter particle UNKNOWN True parameter

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

  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, ~9s • 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. Modulation of +/-2% by Sep. 2009

  11. 2. CoGeNT (Ge) 140kgd Science 332 (2011) 1144 • P-type point contact detector has very low noise thus low energy threshold due to small cap.  smaller-mass DM w/ ionization only PRL 101, 251301 (2008) arXiV1106.06500

  12. Assume all the unknown events from DM Mod. (c2/dof=7.8/12) 80%C.L. accept. Flat (c2/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 Observed data • 3 events remained • 1.8+/-0.6BG expected (28%) Neutron source (causes nuclear recoil) calibration data Nuclear recoil  e/gamma 99.75% rejection line and 3 sigma contour of NR DM search window (8.4-44.6keVnr)

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

  16. Recent “signals” of DM, axion, and n • 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. “Italian signals” Recent “signals” of DM, axion, and n • 2000: DAMA experiment (Gran Sasso) started to claim the observation of dark matter.  >8s 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 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 n 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/7Be) ◎ Xenon neutrino MASS detector (double beta decay) ◎ Xenon detector for Weakly Interacting MASSive Particles (DM search) 100kg FV (800kg) 0.8m, DM First phase • 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. 10ton FV (24ton) 2.5m Solar n, 0nbb, DM in future Y. Suzuki, hep-ph/0008296

  22. Structure of the 800kg detector • Single phase liquid Xenon (-100oC, ~0.065MPa) scintillator • 835kg of liquid xenon, 100kg in the fiducial volume • 642 PMTs • 5keVelectron equiv. (~25keVnuclear recoil) thre.

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

  24. Event reconstruction

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

  26. High light yield and good position resolution • 57Co 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 at various positions Reconstructed energy 122keV +15V DATA MC ~4% rms 136keV 59.3keV (W-Ka) [keV]

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

  28. Expected sensitivity Spin Independent 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. XMASS 5keVee thre. 100d Expected energy spec. CDMSII XENON100 1 year exposure scp=10-44 cm2 50GeV WIMP XMASS 2keVee thre. 100d Black:signal+BG Red:BG

  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 As of Sep. 2010 P-01

  32. Summary • “Positive” signals by DAMA, CoGeNT, and CRESST-II (~10GeV, 10-40cm2) 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 2x10-45cm2 (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 g.

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