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Dark Matter Search with Stilbene Scintillator

Dark Matter Search with Stilbene Scintillator. 9th ICEPP Symposium in Hakuba 20 Feb 2003 Hiroyuki Sekiya University of Tokyo. Dark Matter in the Universe. Flat Universe Ω 　＝　 Ω Ｍ 　＋　 Ω Λ ＝　１. Results of WMAP. 2/12 Asahi.com. COBE & WMAP. Accurate measurements of CBR anisotropies

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Dark Matter Search with Stilbene Scintillator

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  1. Dark Matter Search with Stilbene Scintillator 9th ICEPP Symposium in Hakuba 20 Feb 2003 Hiroyuki Sekiya University of Tokyo

  2. Dark Matter in the Universe Flat Universe Ω　＝　ΩＭ　＋　ΩΛ＝　１

  3. Results of WMAP 2/12 Asahi.com

  4. COBE & WMAP Accurate measurements of CBR anisotropies reveals Ωtot = 1 ΩΛ = 0.73 ΩM = 0.27 Ωbaryonic = 0.04 Ωnon baryonic= 0.23

  5. Neutralino as Dark Matter Non Baryonic Cold Dark Matter Candidate • DM Axion ( KSVZ, DFSZ ) • SUSY WIMPs ( LSP : neutralino ) Leading candidate Neutralino Lowest mass, linear superposition of Photino, zino, higgsino Various implementation of MSSM leads to various Mass window : GeV < < TeV

  6. DM Neutralino Search • Looking for antiprotons, positrons, gamma rays・・・produced by WIMP annihilation in the GALACTIC HALO. BESS, GLAST, ISS, … • Looking for high energy neutrinos as final products of WIMP annihilation in the celestial bodies (EARTH, SUN). SK, AMANDA, MACRO, … • Measuring the nuclear recoil produced by the elastic scattering of WIMP by the DETECTOR nuclei. Ｄｉｒｅｃｔ　Ｓｅａｒｃｈ DAMA, CDMS, UKDMC, TOKYO, …

  7. Signal of WIMPs Earth motion through the galactic halo produce asymmetries distinctive of WIMPs. • Earth orbital motion around the Sun (15 km/s) Annual modulation of the WIMP interaction rate.

  8. Directional Signal • Earth motion around the Galactic Center(230 km /s) Directional asymmetry of the recoil nucleus. WIMP halo manifests as WIMP wind with halo model dependent directional signature. isothermal halo • Directional sensitivity is indispensable for identifying Galactic WIMP signature. • Potential for distinguishing different halo model. WIMP astronomy

  9. Organic Crystal Scintillator Scintillation efficiency depends on direction of nuclear recoils with respect to crystal axes. anthracene stilbene monoclinic system Interesting recoil energy region ( below 100 keV ) had not been investigated.

  10. Carbon Recoils in Stilbene Recoil energies of protons given by WIMPs are too small! We had measured scintillation efficiency of Carbon recoils in a stilbene single crystal. • Light yield : 30% of NaI • λmax : 410 nm • Decay time : 5 ns 2cm x 2cm x 2cm Amcrys-H @Ukraine

  11. Calibration with Neutrons θN Recoil energy : ER Recoil angle : θN θn neutron target crystal are uniquely determined. neutron counter Evisible • Quenching Factor (ER, θN) = ER Performed at 3.2 MV Pelletron accelerator (東工大　原子炉工学研究所　井頭研） • Pulsed proton beam (2 MHz 1.5ns width) • Li(p,n) Be (Q = -1.6MeV) reaction 7 8

  12. A Bird’s Eye View

  13. Li Target

  14. The Detectors

  15. Results 252 • Cf run was also performed. • Depends on the angle with respect to c’ axis. • Variation of • the scintillation • response is • about 7%.

  16. Application to Dark Matter Detector Scattered WIMP VE Recoil directions show a peak at γ= 180° WIMP wind γ Nuclear Recoil Light outputs should be • minimum at c’ // VE. • maximum at c’┴ VE. See the difference in light output spectra.

  17. Possible Measurements 1 Setting on the ground WIMP wind ６°to c’ The earth moves toward constellation Cygnus. (R.A. 21h12.0’, Dec +48.19°) 36° VE 42° 42°to the earth’s axis 78°to c’ WIMP incident angle with respect to c’ axis modulates 72°over 12 sidereal hours at N36°(KAMIOKA)

  18. Possible Measurements 2 c’ axis maintained to the direction of the galactic rotation ( Cygnus )and the galactic center ( Sagittarius ). Set the crystals on the driving system like

  19. Expected Spectra Assuming spherical isothermal halo. • Resemble the annual • modulation of the • count rate. • The measurements can be achieved more robustly. • 100 kg 100 days! (Zero BG) ρ0=0.3 GeV/cm, v0=220 km/s, vE=232km/s

  20. Ability to set an upper limit Assuming 1 counts/keV/day/kg Directional sensitivity also has the advantage of exclusion the parameter space. • More important is • the sensitivity for an actual positive WIMP detection!

  21. Plans • Stilbene 5cmφ x 5cm (100g) x 3 • Low background PMTs R8778 MOD-ASSY • Background measurement @Kamioka underground laboratory • Settings on the turntable or on the ground?? Stronger directional dependency is favorable! naphthalene

  22. Naphthalene 50% anisotropy • Yield : 12% of NaI • λmax : 348 nm • Decay time : 96 ns Available from Ukraine Z. phys. 165 (1961) 1

  23. Summary • The variation of the quenching factor of the stilbene crystal is 7%. • That could produce the possible dark matter signal. • Pilot run with 300g stilbene will be performed at Kamioka underground lab. • Naphthalene crystals which show more anisotropic scintillation response will be ready.

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