Dark Matter Search with Stilbene Scintillator

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Dark Matter Search with Stilbene Scintillator

• 9th ICEPP Symposium in Hakuba
• 20 Feb 2003
• Hiroyuki Sekiya
• University of Tokyo

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Dark Matter in the Universe
Flat Universe O OM O? 1
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Results of WMAP
2/12 Asahi.com
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COBE WMAP
Accurate measurements of CBR anisotropies reveals
Otot 1
O? 0.73 OM 0.27
Obaryonic 0.04 Onon baryonic 0.23
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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 lt lt TeV
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DM Neutralino Search

• Looking for antiprotons, positrons, gamma
  raysproduced 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,
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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.
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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
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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.
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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
• ?max 410 nm
• Decay time 5 ns

2cm x 2cm x 2cm Amcrys-H _at_Ukraine
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Calibration with Neutrons
?N
Recoil energy ER Recoil angle ?N
?n
neutron
target crystal
are uniquely determined.
neutron counter
Evisible

• Quenching Factor (ER, ?N)

ER
Performed at 3.2 MV Pelletron accelerator
(??? ???????? ???)

• Pulsed proton beam (2 MHz 1.5ns width)
• Li(p,n) Be (Q -1.6MeV) reaction

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8
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A Birds Eye View
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Li Target
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The Detectors
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Results
252

• Cf run was also performed.

• Depends on
• the angle with
• respect to
• c axis.

• Variation of
• the scintillation
• response is
• about 7.

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Application to Dark Matter Detector
Scattered WIMP
VE
Recoil directions show a peak at ? 180
WIMP wind
?
Nuclear Recoil
Light outputs should be

• minimum at c // VE.
• maximum at c - VE.

See the difference in light output spectra.
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Possible Measurements 1
Setting on the ground
WIMP wind
6to c
The earth moves toward constellation Cygnus.
(R.A. 21h12.0, Dec 48.19)
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42
VE
42to the earths axis
78to c
WIMP incident angle with respect to c axis
modulates 72over 12 sidereal hours at
N36(KAMIOKA)
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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
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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)

?00.3 GeV/cm, v0220 km/s, vE232km/s
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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!

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Plans

• Stilbene 5cmf x 5cm (100g) x 3
• Low background PMTs R8778 MOD-ASSY
• Background measurement
• _at_Kamioka underground
  laboratory
• Settings on the turntable or on the ground??

Stronger directional dependency is favorable!
naphthalene
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Naphthalene
50 anisotropy

• Yield 12 of NaI
• ?max 348 nm
• Decay time 96 ns

Available from Ukraine
Z. phys. 165 (1961) 1
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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.