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DMTPC: A Dark Matter Detector with Directional Sensitivity Shawn Henderson on behalf of the DMTPC Collaboration TeVPA 2009 July 12, 2009
DMTPC: A Dark Matter Detector with Directional Sensitivity
Shawn Henderson
on behalf of the DMTPC Collaboration
TeVPA 2009 July 12, 2009
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Dark Matter Time Projection Chamber
Boston UniversityS. Ahlen (PI), A. Inglis, H. Tomita
Brandeis UniversityA. Dushkin, S. Goyal, F. Golub, B. N. Skvorodnev, H. Wellenstein (PI)
Massachusetts Institute of TechnologyP. Fisher (PI), G. Sciolla, R. Yamamoto, D. Dujmic, R. Vanderspek, J. Battat, J. Monroe, S. Henderson, A. Kaboth, J. Lopez, T. Caldwell,
A. Lee, T. Sahin, I. Wolfe, H. Yegorian
Detector PapersD. Dujmic et al. [DMTPC] NIMA 584 (2007)A. Kaboth et al. [DMTPC] NIMA 592 (2008)D. Dujmic et al. [DMTPC] Astropart. Phys 30 (2008)T. Caldwell et al. [DMTPC] arXiv:0905.2549 (2009)
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Time Projection Chamber
Side View
GND
+V
-V
Drift 5kV
20 cm
Amplify0.7 kV0.5 mm
Low pressure gas
CF4
~0.1 atm
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GND
+V
-V
Drift 5kV
20 cm
Amplify0.7 kV0.5 mm
Recoil(few mm long)
ER
χ
χ
PMT PMTCamera
photons electrons 9
GND
+V
-V
Drift 5kV
20 cm
Amplify0.7 kV0.5 mm
χ
χPMT PMTCamera
electrons 10
GND
+V
-V
Drift 5kV
20 cm
Amplify0.7 kV0.5 mm
χ
χPMT PMTCamera
photons electrons 11
15.5
cm
15.5 cm
We Measure E
recoil from total light
Direction of track
Sense of direction
For nuclear recoils,
dE/dx DECREASES
along track
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θ
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Reconstructing the Sense
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Particle Identification
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DMTPC 10-liter detector
Dual TPC
Mesh-amplification region (2-D readout)
10-L fiducial volume 20 cm drift 3g at 75 Torr
Charge readout
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BackgroundStudy
Detector stability
Surface (basement) lab Remote operation5-second exposures (shutter-less) Without trigger - every image saved Daily gas refill70% live time 1% gain stability/day 6 and 3 week long datasets 20
( )Energy VS Range No Cuts
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Alphas
Worms
Pro
ject
ed R
ange
(mm
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α Backgrounds
Some are contained in the view field; cut on energy VS range
Little impact on detector efficiency
Most likely from U, Th chains and Rn
Particularly large background because detector materials were not chosen for radiopurity
Most come from the sides and can be identified by edge crossing
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WormsAny event with one or a few localized very bright pixels
CCD-specific background
Probable origin: n's, 's, radioactivity in CCDμ
Rate ~ 7-10 mHz
Cut on high energy densities
Better software/hardware solutions are on the way
Going underground could help
μ
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Analysis energy range: 110-200 keV Measured # BG events: 7 Expected # BG events: 21 Detector live time: 10.8 days Active detector mass: 0.0033 kgThis exposure: 0.036 kg*days
After Cuts
LimitCalculation
PRELIMINARY
PRELIMINARY
PRELIMINARY
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Expected Sensitivity
DMTPC10Lsurface estimate for 7 observed events, 20 bkg expected, 44g-day,E>110keV
PRELIMINARY
KIMS (2007)
COUPP (2008)
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W aste I solation P ilot PlantLow radon level < 7 Bq/m3 1600m water equivalent < 1 event/yr neutron background
Site ofDMTPC
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DMTPC 10-liter detector SD-proton,
50 keV threshold, 365 days
underground @ 100 torr
KIMS (2007)COUPP (2008)
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Looking Ahead: A 1-m3 DetectorG. Sciolla arXiv:0805.2431
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Heavier Targets/Inelastic DM?
D. Finkbeiner arXiv:0906.0002
Heavier targets than CF4 are sensitive to inelastic dark
matter models
Could reconcile DAMA and other SI results
Signal is VERY directional
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