a direction sensitive dark matter detector steve ahlen boston university march 7, 2007
TRANSCRIPT
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A Direction Sensitive Dark Matter Detector
Steve Ahlen
Boston University
March 7, 2007
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Evidence of Non-Baryonic Dark Matter
• Fritz Zwicky, 1933: large velocities of galaxies in Coma Cluster
• Gamow, Alpher, 1940’s and many since: big bang nucleosynthesis limits amount of baryonic matter
• Vera Rubin and others, 1970’s: flat rotation curves of essentially all spiral galaxies
• Bullet cluster, 2006: collision of two clusters of galaxies– Optical: galaxies pass through with small interaction– X-ray: hot gas (10 times mass of visible galaxies) pancakes
due to large interaction– Weak lensing of background galaxies: most mass passes
through with no interaction• Concordance model (cosmic microwave
background, dark energy, large scale structure, inflation, etc.)
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Weakly Interacting Massive Particles (WIMPs)
• Lightest supersymmetric particle is a leading candidate for dark matter
• Isothermal halo of our Galaxy (~ 0.001 c)• Annihilation in Galaxy to make antiprotons• Annihilation in Sun to make neutrinos• Elastic interactions with nuclei
– Many possible reactions (spin-dependent and spin-independent) and cross-sections
– Recoil energy of tens of keV– Rate much less than 1 event / kg / day
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Antiproton Excess in Cosmic Rays in 1981 was interpreted as neutralino annihilation in Galaxy(Silk, J., Srednicki, M., 1984, Phys. Rev. Lett. 50, 624)
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Alpha Magnetic Spectrometer
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Positron Fraction
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If AMS Attached to Space Station
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First Direct WIMP Search in 1987
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DAMA claimed discovery• 100 kg NaI• Pulse shape discrimination separates x-rays from recoils• Annual modulation due to variations in relative velocity of
dark matter particles
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CDMS
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Calibration with gamma and neutron sources
Search at Soudan mine in Minnesota
Ahlen Calculation
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Limit based on 46 kg days exposure
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Occidental College, University of New Mexico, Sheffield University
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30keV F ions in 50mbar CF4 [15]. Typical ion range is about 1mm.
15keV electrons in 50mbar CF4 [16]. Typical electron range is about 30mm.
Range vs Energy is powerful technique for particle ID
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WIMP Wind in Our Galaxy• Dark matter halo large compared to baryonic matter in spiral
galaxy• Solar System rotates about galactic center with speed of 220 km/s• Dark matter particles move isotropically with speeds of a few
hundred km/s
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Cathode Mesh 25 m diam, 250 m pitch 1.0kV
Grounded wire grid 25 m diam, 2 mm pitch
Ground plane
Anode wire plane 100 m diam, 5 mm pitch 2.25kV
CF4 at 37 torr
Alpha source
Window
MIT/BU CF4 Prototype – Summer 2006
Peter Fisher, Marta Lewandowska, Steve Ahlen, Hidefumi Tomita
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35 Successive Images for one second exposures
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Alpha Particle Track Diffusion = 275 microns, Gain = 30,000
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45 degrees relative to wire direction
parallel to wire
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900 MeV proton1 atm
5 MeV alpha1/20 atm
TRIM Calculations
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800 keV alpha1/20 atm
Quick Calculation
800 keV alpha1/20 atm
Detailed Calculation
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100 keV F ions in 50 mbar CF4
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Next Generation Directional Prototypes
• Boston University– Steve Ahlen, Hidefumi Tomita, Debbie Avery, Eric Hazen
• MIT– Peter Fisher, Jocelyn Monroe, Gabriella Sciolla, Dennis
Dujmic, Roland Vanderspek• Brandeis
– Hermann Wellenstein • Will work with DRIFT collaboration to explore
various designs with electronic readout and optical readout
• Head-tail direction sensitivity determined with neutron beams
• Supported by DOE Advanced Detector Research Program and the MIT Kavli Institute for Astrophysics and Space Research
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• Two 25cm x 25cm x (2.5 to 25cm) drift cells
• Anode wire diameter 30 or 50 microns• Wire pitch 2.5 mm• Three Dimension Reconstruction:
– In anode plane by scintillation profiles on one or more wires (1 mm by 0.5 mm resolution for track length)
– Perpendicular to anode plane by phototube pulse shape (1 mm resolution for track length)
Optical Readout
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Cubic meter prototype to follow
• 180 grams CF4• 32 low cost (non-cooled) ccds with fast readout and
lenses inside vacuum chamber• 4 drift zones: each 1 meter by 1 meter by 25 cm
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