Dark Matter Search with Direction Sensitive Scintillators The10th
Dark Matter Search with Direction Sensitive Scintillators The10th ICEPP Symposium February 16, 2004, Hakuba H. Sekiya University of Tokyo Table of Contents Motivations Direction Sensitivity for WIMPs search Detector Anisotropic response of organic single crysta
Results of pilot run Preliminary measurements at Kamioka underground laboratory Summary Future Plans by Y. Shimizu Historyof Dark Matter
Dark Matter changes by decades. Composition of Universe NASA/WMAP Science Team Cold Dark Matter 23% 2003 WMAP Quantity is determined, we want to know Quality Motivation How to distinguish WIMPs from BGs? Realistic distinctive WIMP signals arise from the earths mo in the galactic halo. The annual modulation of event rate is one of the possible WIMP signal caused by earths revolution around the sun. The earths rotation through the galaxy provides WIMP wind.
Most convincing signature would be identified with recoil direction sensitive detector. WIMP Wind of Today WIMP wind Revolution 30km/s Cygnus Sun VE=232 km/s DARK HALO (Maxwellian) 220km/s W N
E Organic single crystals Scintillation efficiency depends on direction of nuclear recoils with respect to crystallographic axes. We focus on the stilbene crystals. Stilbene has an advantage in realizing large single crystal. Light yield : 30% of NaI max : 410 nm Decay time : 5 ns In high energy regions, the response was P. Heckmann et al., Z. Phys 162(1961) 84
precisely measured. Scintillation only efficiency depends on monoclinic system Anisotropy for Carbon Recoils measured the angle/energy dependence of the scintillation icience of carbon recoils in a stilbene crystal using neutro energies of 30 keV to 1MeV. H. Sekiya et al., PLB 571(2003) 132 c 2cm2cm2cm
= Recoil angle with respect to c Response to 5.9 keV X-ray Response to 100 keV carbon recoil dependence was confirmed. Anisotropy for Carbon Recoils The variation of the efficiency is 7 % over the measured energy region. Only 7%, however, the WIMP wind is strong enough! Application to WIMPs Detector The earth moves toward Cygnus
(42to the earths axis) Kamioka 36N If we install the crystal with the c axis towards the North, WIMP incident angle changes 80over 12 Expectedhours moduraltion of today sidereal in 4-6 keV window Moduraltion amplitude Pilot Measurement in Kamioka 116g stilbene crystal
2 low BG PMT read out (Hamamatsu R8778MOD) PMTs cool down -7 by Peltier coolers 2 low BG NaI(Tl) active shields (Horiba, Ltd.) Cryos Beta Ltd., Ukraine Pilot Measurement at Kamioka
OFHC Copper 10cm Lead 15cm Polyethylene 20cm N2 gas for Rn purge 2003 Direction of the Wind November 8 2003 to December 11 200 Variation of the angle between the direction of c axis and the direction of the earths motion
2003 Measured Count Rates The count rate for 4-6 keV of every one hour. 2000 counts/keV/day/kg in 4-6 keV energy window Fourier transformation 1/23.934hours=1 sidereal day white background noise Current Issues 1. Rather high background events Radio isotopes in PMT U-chain Th-chain
1.810-2Bq 6.910-3Bq Ge spectrometry K 1.410-1Bq Co 5.510-3Bq Although NaI(Tl) worked effectively, highly radio-pure device is needed in principle.
(Special material-selected PMT or avalanche photo diode 2. Stilbene itself. SI p A2 Organic material contains only proton or Anisotropy is limited to 7%. 12 C. Future Prospects Spin dependently interacting WIMPs serch with fluorine loaded organic crystals. Octafluoronaphetalene SD p J ( J 1) M.P.
C10F8 = 87 max= 350 nm crystalline powder Expected Sensitivity with C10F8 Summary We focused on anisotropic scintillation detector wi organic single crystals for dark matter search. The response of carbon recoils in a stilbene crysta in interested energy region was measured and the sensitivity to WIMPs was investigated. We have performed pilot measurements in Kamioka
Underground laboratory, which presents a new method of dark matter search and the start point of the developments. We proposed new target (octafluoronaphetalene) for SD interacting dark matter.
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