updates from the dark matter time projection …ppnewage/cygnus2013/session/...updates from the dark...

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

1

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)

3

Gallery of DMTPC Detectors 10L

Underground at WIPP

4Shooter (20L)

At MIT Under development

DMTPCino (m3)

4

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

5

3x x4

CF4 @ 75 Torr

3x 4x

GND

Anode Veto

Mesh

All sensors outside of active volume

6

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.

7

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

9

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)

10

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%.

12

Gain limited by streamer discharges

Typical operating point 60 Torr, 670V Gain = 63,000

13

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

14

Lesson 3: Recoils can trigger sparks

15

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

16

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%.

17

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)

18


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)

19


AD

U

As expected, the energy calibration depends on amplification region voltage (gas gain), but not on alpha source height (diffusion)

20

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

21

Track reconstruction in mosaic image

22

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

23


24 (CCD image is just to illustrate point)


not y0

y1 y0

y1

25 y0 y1 so


indistinguishable from

y0

y1 y0

y1

26

Track fitting with confidence: next steps

•  Evaluate benefits of restricting DM analysis to “high confidence” tracks only?

•  Extend the track fitting to 2D

27

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

28

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*


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

150

200

s]µTime [-2 0 2 4

Volta

ge [m

V]

-50

0

50

100

150

200

U.*of*Colorado*Seminar*

Mesh*(Current*Signal)*Readout*100*keVee**Nuclear*Recoil*(Signal)*

100*keVee*

ElectronZLike*Event*(Background)*


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

50

100

150

200

s]µTime [-2 0 2 4

Volta

ge [m

V]

-50

0

50

100

150

200



100*keVee*



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"



s]µTime [-2 0 2 4

Volta

ge [m

V]-50

0

50

100

150

200

s]µTime [-2 0 2 4

Volta

ge [m

V]

-50

0

50

100

150

200



100*keVee*



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"



Nuclear recoil Electron recoil

s]µTime [-2 0 2 4

Volta

ge [m

V]

-50

0

50

100

150

200

s]µTime [-2 0 2 4

Volta

ge [m

V]

-50

0

50

100

150

200



100*keVee*



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"



30

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

0

50

100

150

200

25%

75%

Rise Time = T(75%)-T(25%)

Pulse*Shape*• Rise*Time*(above)*• Pulse*Height*• Pulse*Width*• Etc.*


Background*Rejec7on*with*Pulse*Shape**

Nuclear*Recoils*

Electrons,*MIPs,*etc.*

Preliminary*


eZ*rejec7on*with*smaller*detector*be:er*than*1.1x10Z5*for*combined*charge*+*CCD*analysis*J.P.#Lopez#et#al.,#NIM#A696#(2012)#1219128.#

32

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

33

Charge background spectra

34

See MIPs in high rise-time events

35

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)

36

(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

39

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

0.6

0.7

0.8

0.9

1

Angle: 5 degα

Angle: 25 degα

H/T sensitivity appears to “turn on” when range ~ 3*diffusion

41

DMTPCino (1 m3)

42

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

43

4sh u/g

DMTPCino (m3) u/g

Thank you

44

updates from the dark matter time projection …ppnewage/cygnus2013/session/...updates from the dark...

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