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transcript
Updates from the Dark Matter Time Projection Chamber Group (DMTPC)
Cygnus 2013 Workshop on Directional Dark Matter Detection Toyama, Japan 2013 June 10
James Battat (Wellesley College) for the DMTPC collaboration
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DMTPC Collaboration
Brandeis University A. Dushkin, H. Wellenstein*
Bryn Mawr/Wellesley T. Ananna, E. Barbosa de Souza, J. Battat*, V. Gregoric, K. Recine,, L. Schaefer
University of Hawaii I. Jaegle, S. Ross, S. Vahsen*
MIT H. Choi, C. Deaconu, P. Fisher*, S. Henderson, W. Koch, J. Lopez, H. Tomita!
Royal Holloway (UK) G. Druitt, R. Eggleston, P. Giampa, J. Monroe*
*=PI, postdoc, grad student, undergrad 2
Gallery of DMTPC Detectors 10L
Underground at WIPP
4Shooter (20L)
At MIT Under development
DMTPCino (m3)
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Gallery of DMTPC Detectors 10L
Underground at WIPP
4Shooter (20L)
At MIT Under development
DMTPCino (m3)
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4Shooter Overview
• 20L (4.5g F) • Higher vacuum (10-5 torr)
between fills • Material selection
(OFHC copper, acetal, stainless steel, G-10)
• 4 CCD cameras, 3 PMTs, 3 charge readout channels
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3x x4
CF4 @ 75 Torr
3x 4x
GND
Anode Veto
Mesh
All sensors outside of active volume
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4Shooter Schematic
Improved Field Cage (spacers), and amplification region fabrication scheme ! More gain, lower spark rate. Repeatable amplification region construction technique in a clean-room environment.
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vs.
4shooter 10L
4Shooter Construction
Lower alpha background rate & better tagging capability
Raw � rate is 19x lower 10L 210 mHz 4sh 11 mHz
And 4sh field cage has 3x more internal surface area
10L field of view 8
4sh mosaic image
10L: inferred alpha start points
4sh gas gain measurements
Typical operating point 60 Torr, 670V Gain = 63,000
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Lesson 1: gain degradation vs. time
Time [hours since start]0 5 10 15 20 25
Gai
n
69500
70000
70500
71000
71500
72000
72500
73000
4sh over 1 day (~3% drop) Cylon over 200 days (20% drop then stable)
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Gain degradation over time is well-known
Initial gain decay is well-known and seen in many detectors. For example: Kadyk 1998 (SLAC Detector Techniques Lectures) http://www-group.slac.stanford.edu/sluo/lectures/Detector-Lectures.html 11
Lesson 2: gain decreases with x-ray flux Likely due to space-charge in amplification region
Gai
n (a
rbitr
ary
units
)
Layers of Aluminum Foil
Increasing x-ray flux
Calibration with a strong source can underestimate the gas gain by ~30%.
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Gain limited by streamer discharges
Typical operating point 60 Torr, 670V Gain = 63,000
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Sparking and Raether limit
• “Raether’s criterion: a spontaneous transition from avalanche to streamer, followed by a discharge, when the avalanche size reaches a value of a few 107.”
• “In multiple structures, where the gain is shared between two devices in cascade, the maximum overall gain under irradiation is increased by at least one order of magnitude; we speculate this to be a consequence of a voltage dependence of Raether’s limit, larger for low operating potentials.”
A. Bressan et al., Nuclear Instruments and Methods in Physics Research A 424 (1999) 321—342
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Lesson 3: Recoils can trigger sparks
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75 Torr CF4
If electron density is too high, the avalanche becomes a streamer, rendering the detector insensitive. In practice, compact (low-drift) tracks preferentially generate streamers/sparks. The lower part of the TPC is not “active” anymore! Also this can lead to an angular dependence as well (vertical tracks lead to sparks)
High gain tracks are more diffuse (long drift)
Low gain
0
50
100
150
200
550 600 650 700 750 800
elec
tron
gai
n (x
1,0
00)
anode voltage (V)
Electron Gain in the amplification region measured with 241Am Į tracks in 40 torr CF4 gas
406 um 508 um 610 um 711 um 813 um 1016 um
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Diffusion vs. amplification gap size
-10 -8 -6 -4 -2 0 2 4 6 8 100
10
20
30
40
50
Projected alpha tracks well fit by double (not single) gaussian
As gap doubles, the core is unchanged, but wings widen by 25%.
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CCD Energy Calibration
One 241Am for each camera. Side question: do 241Am x-rays degrade the gain? (59 keV from 241Am, plus 14, 17, 21 keV lines from 237Np)
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CCD Energy Calibration
AD
U
Data MC Tune electron diffusion and
“gain” (ADU/keVee) until MC matches data (for transverse and longitudinal projections).
Average of projections for many tracks (single camera)
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CCD Energy Calibration
AD
U
As expected, the energy calibration depends on amplification region voltage (gas gain), but not on alpha source height (diffusion)
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Spatial variation in detector response
57Co 122 keV � MFP = 4 m
Each of the 4 cameras has a smooth rotational symmetry to the gain pattern. The amplification region (especially the spacers) shows higher-frequency variations
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Track reconstruction in mosaic image
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Track fitting with confidence
Make use of the known profile of a NR (from the Bragg curve) to (1) fit for the Head/Tail and (2) assign a confidence in the H/T determination
convolved with gaussian
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Track fitting with confidence
24 (CCD image is just to illustrate point)
Track fitting with confidence
not y0
y1 y0
y1
25 y0 y1 so
Track fitting with confidence
indistinguishable from
y0
y1 y0
y1
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Track fitting with confidence: next steps
• Evaluate benefits of restricting DM analysis to “high confidence” tracks only?
• Extend the track fitting to 2D
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Fit function
-10 -5 0 5 10-10
-5
0
5
10
0
0.51
1.52
2.5
3
3.54
DmtpcMath::lineSegmentConvolvedWithGaussian2D
Cosmin Deaconu (MIT) Reconstruction Update June 6, 2013 19 / 20
Nuclear recoil model
Charge readout: going beyond energy reconstruction
Anode Veto
Mesh
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Brief reminder about the three charge channels
x-y position information from charge alone (useful in ccd/charge matching)
U.*of*Colorado*Seminar*x [cm]
-15 -10 -5 0 5 10 15
y [c
m]
-15
-10
-5
0
5
10
15
Anode / Veto
Anode*(Charge*Integra7ng)*Readout*
Preliminary*
39*Jeremy*P.*Lopez,*MIT*
Central*Event*
Edge*Event*
Central*anode*channel*
Veto*channel*
Energy*Loss*
Posi7on*
Energy*Loss*
U.*of*Colorado*Seminar*x [cm]
-15 -10 -5 0 5 10 15
y [c
m]
-15
-10
-5
0
5
10
15
Anode / Veto
Anode*(Charge*Integra7ng)*Readout*
Preliminary*
39*Jeremy*P.*Lopez,*MIT*
Central*Event*
Edge*Event*
Central*anode*channel*
Veto*channel*
Energy*Loss*
Posi7on*
Energy*Loss*
7
3
29
Event discrimination based on mesh pulse shape s]µTime [
-2 0 2 4
Volta
ge [m
V]
-50
0
50
100
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s]µTime [-2 0 2 4
Volta
ge [m
V]
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U.*of*Colorado*Seminar*
Mesh*(Current*Signal)*Readout*100*keVee**Nuclear*Recoil*(Signal)*
100*keVee*
ElectronZLike*Event*(Background)*
40*Jeremy*P.*Lopez,*MIT*
Mesh Fast Readout
!"#$
%&'$
($)*)+)(,-%$
%&'$./('$
%+%,01/('$,/++%,0%2$34.,5+6$7('8$
$./('$
)*)+)(,-%$./('$0)5%$+/(9%1$7:'8$;%,)4'%$/<$=#>$./($?/;.+.06$
@.?%$('$ :'$
=411%(
0$ ./('$%&$ AB$
C.'%$D?%$/<$%&$,411%(0$$E4+'%$2%E%(2'$/($01),5$AB$
$F!$
Mesh Fast Readout
!"
#$%&"'("
)*++&,
-"
.$(&"/%&"01"&2"3*++&,-"4*5(&""%*36"7$8&+"$,"/%&"10+"!9("
"
:;"
&2"
!"&,&+<="8&40($/0,"%*36"5&(("(4>/>55="503>5$?&8""@0+&"5$A&5="-0"8&40($-"&,&+<="$,"B&-0"
CD"
Now:*Used*for*background*rejec7on*
Future:*Help*achieve*3D*angle*reconstruc7on*
s]µTime [-2 0 2 4
Volta
ge [m
V]
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s]µTime [-2 0 2 4
Volta
ge [m
V]
-50
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U.*of*Colorado*Seminar*
Mesh*(Current*Signal)*Readout*100*keVee**Nuclear*Recoil*(Signal)*
100*keVee*
ElectronZLike*Event*(Background)*
40*Jeremy*P.*Lopez,*MIT*
Mesh Fast Readout
!"#$
%&'$
($)*)+)(,-%$
%&'$./('$
%+%,01/('$,/++%,0%2$34.,5+6$7('8$
$./('$
)*)+)(,-%$./('$0)5%$+/(9%1$7:'8$;%,)4'%$/<$=#>$./($?/;.+.06$
@.?%$('$ :'$
=411%(
0$ ./('$%&$ AB$
C.'%$D?%$/<$%&$,411%(0$$E4+'%$2%E%(2'$/($01),5$AB$
$F!$
Mesh Fast Readout
!"
#$%&"'("
)*++&,
-"
.$(&"/%&"01"&2"3*++&,-"4*5(&""%*36"7$8&+"$,"/%&"10+"!9("
"
:;"
&2"
!"&,&+<="8&40($/0,"%*36"5&(("(4>/>55="503>5$?&8""@0+&"5$A&5="-0"8&40($-"&,&+<="$,"B&-0"
CD"
Now:*Used*for*background*rejec7on*
Future:*Help*achieve*3D*angle*reconstruc7on*
s]µTime [-2 0 2 4
Volta
ge [m
V]-50
0
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200
s]µTime [-2 0 2 4
Volta
ge [m
V]
-50
0
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100
150
200
U.*of*Colorado*Seminar*
Mesh*(Current*Signal)*Readout*100*keVee**Nuclear*Recoil*(Signal)*
100*keVee*
ElectronZLike*Event*(Background)*
40*Jeremy*P.*Lopez,*MIT*
Mesh Fast Readout
!"#$
%&'$
($)*)+)(,-%$
%&'$./('$
%+%,01/('$,/++%,0%2$34.,5+6$7('8$
$./('$
)*)+)(,-%$./('$0)5%$+/(9%1$7:'8$;%,)4'%$/<$=#>$./($?/;.+.06$
@.?%$('$ :'$
=411%(
0$ ./('$%&$ AB$
C.'%$D?%$/<$%&$,411%(0$$E4+'%$2%E%(2'$/($01),5$AB$
$F!$
Mesh Fast Readout
!"
#$%&"'("
)*++&,
-"
.$(&"/%&"01"&2"3*++&,-"4*5(&""%*36"7$8&+"$,"/%&"10+"!9("
"
:;"
&2"
!"&,&+<="8&40($/0,"%*36"5&(("(4>/>55="503>5$?&8""@0+&"5$A&5="-0"8&40($-"&,&+<="$,"B&-0"
CD"
Now:*Used*for*background*rejec7on*
Future:*Help*achieve*3D*angle*reconstruc7on*
Nuclear recoil Electron recoil
s]µTime [-2 0 2 4
Volta
ge [m
V]
-50
0
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100
150
200
s]µTime [-2 0 2 4
Volta
ge [m
V]
-50
0
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100
150
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U.*of*Colorado*Seminar*
Mesh*(Current*Signal)*Readout*100*keVee**Nuclear*Recoil*(Signal)*
100*keVee*
ElectronZLike*Event*(Background)*
40*Jeremy*P.*Lopez,*MIT*
Mesh Fast Readout
!"#$
%&'$
($)*)+)(,-%$
%&'$./('$
%+%,01/('$,/++%,0%2$34.,5+6$7('8$
$./('$
)*)+)(,-%$./('$0)5%$+/(9%1$7:'8$;%,)4'%$/<$=#>$./($?/;.+.06$
@.?%$('$ :'$
=411%(
0$ ./('$%&$ AB$
C.'%$D?%$/<$%&$,411%(0$$E4+'%$2%E%(2'$/($01),5$AB$
$F!$
Mesh Fast Readout
!"
#$%&"'("
)*++&,
-"
.$(&"/%&"01"&2"3*++&,-"4*5(&""%*36"7$8&+"$,"/%&"10+"!9("
"
:;"
&2"
!"&,&+<="8&40($/0,"%*36"5&(("(4>/>55="503>5$?&8""@0+&"5$A&5="-0"8&40($-"&,&+<="$,"B&-0"
CD"
Now:*Used*for*background*rejec7on*
Future:*Help*achieve*3D*angle*reconstruc7on*
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PID with Mesh Readout (different detector)
The last 75 keVee of an 241Am �
137Cs � 60 keVee
Demonstrated rejection of 137Cs �’s between 40 keVee < E < 200 keVee of 105 (90% CL upper-limit) using CCD+veto+mesh
R&D Data
R&D Data
R&D Data
J. Lopez et al. NIMA 696, 2012 31
4sh data looks even better (though analysis ongoing)
s]µTime [-0.5 -0.4 -0.3 -0.2
Volta
ge [m
V]
-50
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200
25%
75%
Rise Time = T(75%)-T(25%)
Pulse*Shape*• Rise*Time*(above)*• Pulse*Height*• Pulse*Width*• Etc.*
U.*of*Colorado*Seminar*
Background*Rejec7on*with*Pulse*Shape**
Nuclear*Recoils*
Electrons,*MIPs,*etc.*
Preliminary*
48*Jeremy*P.*Lopez,*MIT*
eZ*rejec7on*with*smaller*detector*be:er*than*1.1x10Z5*for*combined*charge*+*CCD*analysis*J.P.#Lopez#et#al.,#NIM#A696#(2012)#1219128.#
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Charge background spectra Full Spectra
]ee
Energy [keV1 10 210
]-1
s-1 ee
Rat
e [k
eV
-610
-510
-410
-310
-210
-110
1
10
75 torr60 torr45 torr
MIP Peaks
-2.15E∝
-6.36E∝
Knee
Ankle
not contained-e
Low E rise
Figure: Above ankle, few electrons, but not mostly ↵s or nuclear recoils.
Jeremy Lopez (MIT LNS) Update on Background Data 24 April 2013 8 / 11
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Charge background spectra
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See MIPs in high rise-time events
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Data expected to be wider due to detector resolution, angular distribution, and possible multi-particle events. Simulation is vertical only.
Nuclear recoil directional sensitivity analysis underway (with AmBe source)
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(MIT Ph. D. thesis to be submitted inAugust)
Direction reconstruction at low energy
Only the tail end of the alpha track makes it into the active region ! low energy recoils. 37
All tracks drift full length Smaller dE/dx than NR
Direc7onality*with*Alphas*
U.*of*Colorado*Seminar* 36*Jeremy*P.*Lopez,*MIT*
77*keVee*
148*keVee*
117*keVee*
211*keVee*
Sample low-energy alpha track images
38
Directionality with low-energy alpha tracks
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40
Direc7onality*with*Alphas*
U.*of*Colorado*Seminar* 36*Jeremy*P.*Lopez,*MIT*
77*keVee*
148*keVee*
117*keVee*
211*keVee*
Range [mm]0 2 4 6 8 10 12 14 16
Fra
ctio
n w
ith C
orre
ct H
ead
Tail
0
0.1
0.2
0.3
0.4
0.5
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0.8
0.9
1
Angle: 5 degα
Angle: 25 degα
H/T sensitivity appears to “turn on” when range ~ 3*diffusion
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DMTPCino (1 m3)
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Amplification region = triple-mesh One camera images two TPCs Detector will fit in existing underground laboratory at WIPP Triple mesh prototype built and under test now. Vessel fabrication expected in the Fall.
Year2004 2006 2008 2010 2012 2014
]2 [c
mSD
-pσ
-4010
-3910
-3810
-3710
-3610
-3510
-3410
-3310
-3210
-3110
DRIFT II
DMTPC 10L (surf)NEWAGE
surf u/gCOUPP
SIMPLE
PICASSO
NAIAD
XENON100
XENON10
CDMS
KIMS
Spin-dependent (proton) limits vs. time
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4sh u/g
DMTPCino (m3) u/g
Thank you
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