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RESCEU 2003 9 2 Slide 2 Composition of the Universe Results of WMAP Slide 3 2/12 Asahi.com Slide 4 Neutralino as Dark Matter DM Axion ( KSVZ, DFSZ ) SUSY WIMPs ( LSP : neutralino ) Non Baryonic Cold Dark Matter Candidate Leading candidate Lowest mass, linear superposition of Photino, zino, higgsino Various implementation of MSSM leads to various Mass window : GeV < < TeV Neutralino Slide 5 DM Neutralino Search Looking for antiprotons, positrons, gamma rays produced by WIMP annihilation in the GALACTIC HALO. BESS, GLAST, AMS, 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. DAMA, CDMS, UKDMC, TOKYO, Slide 6 Tokyo Group Dark Matter Search Projects LiF / NaF bolometer for SPIN DEPENDENT interacting neutralino search. Present collaborator M. Minowa, Y. Inoue, H. Sekiya, Y. Shimizu, W. Suganuma (University of Tokyo) Recoil direction sensitive organic crystal scintillator for WIMP wind detection. Slide 7 1 LiF / NaF Bolometer K. Miuchi et al., Astropart. Phys. 19 (2003) 135 A. Takeda et al., Submitted to Phys. Lett. B Slide 8 Motivation Neutralino-nucleus cross section Reduced mass Fermi coupling constant Isotopeunpairedabundance 2 J(J+1) 19 Fp100%0.647 7 Lip92.5%0.411 23 Nap100%0.041 73 Gen7.8%0.065 127 Ip100%0.023 Enhancement factor If only either proton or neutron contribution is considered, SD interaction term. :Land factor J :Total spin in the nuclei 19 F has the largest 2 J(J+1) Odd group model Slide 9 Motivation More precisely If contributions of both proton and neutron are considered, a p a n : -nucleon coupling N nucleon spin N in the nucleus N 19 F has opposite sign of N / N compared to 22 Na, 73 Ge, 127 I. 2 parameters should be determined. IsotopeJ N 19 F1/20.441-0.109 7 Li3/20.4970.004 23 Na3/20.2480.020 73 Ge9/20.0090.372 127 I5/20.3090.075 19 F fills the unique role for a p, a n determination. D.R.Tovey et.al., PLB 488 (2000) 17 Slide 10 Detector NTD Ge thermistor is glue to the LiF / NaF crystal which is cooled down 10mK. The thermistor is biased through load register, and the voltage change across the thermistor is fed to the voltage sensitive amplifier placed at the 4K cold stage. Slide 11 Detector NTD thermistor OFHC copper NaF Crystal Bolometer array consists of 8 crystals and NTD thermistors. Each crystal is 2cm2cm2cm. 1 of 2 stages Total mass LiF array 168g NaF array 176g Slide 12 Shields Old lead* Old lead 200 years old for LiF run 400 years old for NaF run Slide 13 Depth 2700 m.w.e (1000 m) Muon flux 10 -7 cm -2 s -1 Measurement at Kamioka Dark Matter Slide 14 Measurement at Kamioka Installation started in Nov. 1999 LiF run: 22 Nov. 2001- 12 Jan. 2002 NaF run: 23 Dec. 2002 24 Jan. 2003 Slide 15 Obtained Energy Spectra Total exposure : 4.1 kg days (LiF) 3.4 kg days (NaF) The spectra look quite similar and the BG rate is about 10-30 counts/keV/day/kg in this energy region. It is quite likely that the remaining background is due to radioactive impurities in the OFHC copper holder or the NTD thermistor. Slide 16 Results SD -p limits DM 0.3 GeV cm -3 v0v0 220 km s -1 v esc 650 km s -1 v Earth 217 km s -1 Astrophysical parameters Best limits (90% C.L.) SD: 23pb for 40GeV Assuming all events are -proton events. Best bin method. Slide 17 Results SD limits in the a p -a n plane We derived the ap-an limits from the cross section limits. We compared with the UKDMC because they provided the limits from Na and I respectively. Although BG rate is still high, we killed more than 2/3 of the parameter space allowed by UKDMC for 50 GeV WIMP because of 19 F. Slide 18 2. Organic Crystal Scintillator Y. Shimizu et al., Nucl. Instr. Meth. A 469 (2003) 347 H. Sekiya et al., to be published in Phys. Lett. B Slide 19 Motivation Realistic distinctive WIMP signals arise from the earth s motion in the galactic halo. Annual modulation of event rate is one of the possible WIMP signal caused by earth s revolution around the sun (30km/s). The earth s velocity through the galactic halo (230km/s) provides more convincing signature of the WIMP. WIMP signature would be identified by direction sensitive detector. WIMP wind is blowing on the earth! Sun 230km/s isothermal halo Slide 20 Detector Scintillation efficiency of organic single crystal depends on direction of nuclear recoils with respect to crystallographic axes. We had measured this property of the stilbene crystal because of its availability. stilbene monoclinic system Light yield : 30% of NaI max : 410 nm Decay time : 5 ns Slide 21 Detector 2cm x 2cm x 2cm 55 Fe 5.9 keV spectrum using PMT (HAMAMATSU R329) Actual light output : 2 p.e/keV Slide 22 Calibration with neutrons Carbon recoils would be effective in detecting WIMPs with interesting mass region. We had measured the recoil angle/energy dependency of carbon recoils in the stilbene single crystal with neutrons. target crystal NN nn Recoil energy E R and Recoil angle N are uniquely determined by kinematics. E visible ERER Methods Relative efficiency (E R, N ) = incident neutron energy E n scattered neutron energy E n with fixed scattered angle n neutron counter Slide 23 Calibration with neutrons 7 Li(p,n) 7 Be using 3.2 MV Pelletron accelerator Two neutron sources are employed. Low energy region precisely (40 keV < E R