Micromesh%20Detector%20for%20DMTPC

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Micromesh Detector for DMTPC

• Denis Dujmic (MIT)
• DMTPC
• Jun 12, 2009

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Outline

• Micromesh detector for low-momentum recoils
• CF4 Parameters?
• How to define head-tail quality?

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DMTPC - Cygnus 2007
S.Ahlen, P.Fisher et al DMTPC Coll.

• Demonstration of low-momentum recoil detection
• CF4 as counting gas
• (?2J(J1)0.74)
• CCD readout
• Head-tail
• Gamma rejection

Multi-wire proportional chamber (MWPC)
Scaling?
Anode3kV Drift 600v/cm CF4 pressure 150-300Torr
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Scaling Problems Point Resolution
D.Dujmic et al. DMTPC NIM A584 (2007)
1D image of fluorine recoil in MWPC
Anode wires
Neutron (or WIMP)

• Problems
• Directionality
• Background rejection

5mm pitch
below 2mm very hard for large areas
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Scaling Problems Gain
Me??dx
Requirements on fiducial volume/gain (MWPC
0.002 liter) - Background study 10 liter -
Improve SD WIMP limits 103 liter (1m3) - Explore
MSSM models 105 liter (100m3)
E field (V/cm/Torr)
Need better gain!
Electron gain ?gt0
Electron loss??lt0 (other colors)
- Reduce alphalt0 region (mm) - Spread charge
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Possible Alternatives
Micropattern detectors, e.g. - Microgap
Angelini, NIMA335 (1993) 69 - Gas electron
multiplier (GEM) - Sauli NIMA386 (1997) 531 -
Micromegas - Giomataris et al.NIMA376 (1996) 29
Mesh
Scintillation?? Demonstrated at high fields (100
kV/cm) Enough photons at 10 kV/cm???
Pitch reduced (5mm -gt256 ?m)
Loss region reduced (mm -gt10s ?m)
Mesh
e-
e-

Anode
Charge spread in 2D
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Micromesh gaseous detector(Micromegas)
CAST COMPASS DMTPC HELLAZ MIMAC T2K ILC
RD DRIFT RD ATLAS RD

• Neutron detection
• CF4He3 CERN/SPSC 99-8 (1999)
• CF4He3He4 (US patent 61/124,61)
• - Ar(or He)isobutane ADS, NIMA562
• x-ray detection
• - Medipix (MM coupled with CMOS)
• - BaF2CSI coating

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Charge Amplification Plane for 10 liter Prototype
SS or Cu mesh
e-
SS ring
G10
Resistive separators (fishing lines) dia0.5mm,
every 2.5cm
28cm
CCD readout area
D.Dujmic et al., Astropart. Phys. 30 (2008) 58
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Image of Alpha Track
OLD (MWPC)
NEW (Mesh)
20x smaller pitch 13x higher gain
successful demonstration of all-mesh and
ITO-mesh amplification
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Neutron-induced Recoils
neutrons
Exposure to Cf-252 neutrons
5mm
D.Dujmic et al., Astropart. Phys. 30 (2008) 58
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Size?
gt90cm
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Charge Gain
75Torr
Charge on anode using Fe55 source
Measure
Sparks
Anode (V)
M (Vout/1.4pC/V) / (5.9keV/W)
W54eV (!)
M gt105 at current operating pressure (75Torr) !
Sparks not a problem
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CCD Readout
CCD Noise
Total light output
ADU/keV
ADU/noise
F
a
e-
Increasing gain with lower pressure
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Energy Resolution
dE dx
15.5cm
?E/E
10cm
241Am
15 at 50keV CCD readout
5.5MeV alpha from 241Am
10 at 5.9keV charge readout
100Torr
15.5cm
Expected fluctuation (avalanche primary)
10 AvalancheAlkhazov, NIM89 (1970) 155,
primaryPoisson
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CF4 Parameters?(Unambiguous measurement of CF4
parameters using directional dark matter
detector)
Review L.G.Christophorou, J.K.Olthoff,
Fundamental Electron Interactions with Plasma
Processing Gases, Plenum (2004)
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Electron Diffusion in CF4?
Average energy of electrons gt10x discrepancy in
measurements in our range-of-interest
E/N Td
Large impact on spatial resolution
?2 (D/?) 2z/E
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Measurement
5 alpha sources at different heights Measure
width as a function of height
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Diffusion Measurement
T.Caldwell, T.Sahin, H. Yegorian, D.D. et al
DMTPC arXiv0905.2549
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Resolution at 20cm
To preserve 1mm resolution Maximum drift length
20cm Optimum drift field 300V/cm (5800V)
300 V/cm _at_75 Torr
?2 (D/?) 2z/E
1mm
150?m
98nbin ? 80 ? 256/121/2 ? (D/? 2z/E)1/2
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Attenuation
?
Attachment to CF4
e.g. e-CF4?CF4-?CF3 F- e-CF4?CF4-?CF3-
F e-CF4?CF4-? F- CF2 F
From previous measurements 0 loss, or 70
loss after 20cm of drift length?
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Attenuation
Position from Fe-55 source at different heights, z
f(z)?
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Head-Tail Quality?
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Quantifying Head-Tail

• How head-tail is quantified is irrelevant
• E.g.
• DMTPC uses skewness of ionization intensity along
  track
• DRIFT uses integrated charge from track halves

However, one should be able to define a common
quality of HT assignment to allow comparison of
detector technologies, provide input to theorist
and sensitivity predictions
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Head-Tail Quality
Single-event HT quality
Dilution due to wrong assignments
Efficiency
Asymmetry
Error on asymmetry
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Head-Tail Quality
(Ngood-Nwrong)/(NgoodNwrong) by DRIFT
Currently, we are not comparing same things
DMTPC
Perhaps, we should decide on common variable
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