TAUP2007, Sendai September 13, 2007

Progress in directional Dark Matter detection:

Observation of Head-Tail Effect with Low-energy

Neutrons

Progress in directional Dark Matter detection:

Observation of Head-Tail Effect with Low-energy

Neutrons

TAUP2007, SendaiSeptember 13, 2007

Denis Dujmic forthe DMTPC collaboration

September 13, 2007 TAUP2007, Sendai 2

OutlineOutline

1. Detector & DMTPC Collaboration2. Calibration with alpha tracks3. Neutron beam results


Dark Matter TPC Collaboration

Dark Matter TPC Collaboration

Boston U.S. Ahlen, M. Lewandowska, A. Roccaro, H. Tomita

Brandeis U.H. Wellensten. N. Skvorodnev

MITB.Cornell* 1), D.Dujmic, W.Fedus*, P.Fisher, A.Kaboth,

G.Kohse, R.Lanza, J.Monroe, A.Piso*, T.Sahin*, G.Sciolla, R.Vanderspek, R.Yamamoto,

H.Yegoryan*

*) undergraduate student1) Also Harvard U.

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MotivationMotivationA. Zero-background analysis hard with ton-size detectors(e.g. coherent scattering from solar neutrinos[Monroe,Fisher,arXiv:0706.3019])

B. Unambiguous proof by correlating DM signal with astrophysical phenomena

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Detection Principle Detection Principle

FF

E e-

0V

+3kV

1. Ionization- low-energy ionization profile?

2. Drift- electron diffusion spread?

3. Amplification, scintillation- gain? energy resolution?

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50Torr

CCDcamera

CCDcamera





total

electronic




Detector PrototypeDetector Prototype

CCD CameraKodak KAF0401 chip768x512 (9x9mm)Cooled (-20C)Photographic lens (55mm)Finger Lakes Instrumentation

Drift region:2.6cm, E=580V/cmAmplification region:Anode: 5mm pitch, 100mGround: 2mm pitch, 50m

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CF4 gas100-380Torr




241 Am

280Torr of CF4

5.5MeV alpha tracks

Bragg peak



280Torr

300Torr

320Torr

340Torr

360Torr380Torr



Scintillation Profile of Track Scintillation Profile of Track

Data vs. SRIMData vs. SRIM





380Torr

340Torr

280Torr


Diffusion Along WireDiffusion Along WireCritical parameter since range for nuclear recoils ~ mmFour alpha sources at different heights in drift region (z)



€

σ[μm]=324 ⊕36 ΔzMaximum size of drift region

340m for z=1cm670m for z=25cm

200Torr

0.5mm 1.05mm 1.6mm 2.05mm






Gain, Energy ResolutionGain, Energy Resolution

Calibration of gain, energy resolution with 5.5MeV ’s from Am-241



Light intensity for alphas crossing a wire

0 tracks

1 track

2 tracks

150-350Torr

• E/E: ~9-15%• gain: <25 ADU/keV• stability: ~1/2day (without flowing gas)• 100-400Torr



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Neutrons vs. WIMPsNeutrons vs. WIMPs• Neutron elastic scattering mimics dark matter recoils

Fluorine recoil energyFluorine recoil angle wrt wires

Fluorine recoil momentum better aligned with WIMP

direction


neutrons

Neutron Beam SetupNeutron Beam Setup

D + T He+n(14.1Me

V)

Anode wires


Head-Tail Effect!Head-Tail Effect!



Wires at 0 deg:

Wires at 180 deg: Direction of

neutrons

arXiv:0708.2370




Measure of Head-Tail EffectMeasure of Head-Tail EffectSkewness of light asymmetry along segment:



< 0forward

> 0backward

Direction tag:

(dimensionless)

Recoil direction

Recoil direction




Head-Tail ResultsHead-Tail Results

backward(26±4)%

forward(74±4)%

Filled - wires@0 degHollow- wires@180 deg

Recoil direction:


Head-Tail ResultsHead-Tail ResultsFraction of recoils in direction of neutrons:


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F =N−

N + +N−




Head-Tail SimulationHead-Tail Simulation±1σ spread in data (points), MC (dashed,shaded)

forward

backward




Energy vs. RangeEnergy vs. RangeCorrelation between energy (ADC counts) and range (CCD bins):

(Slope proportional to stopping power)

Filled - wires@0 degHollow- wires@180 deg


Control SamplesControl Samples• Null test with neutrons perp. to wires•Same # of recoils to left, right



left to right(47.3±2.5%)

right to left(52.7±2.5%)

F F

n

Skewness:<>=0.032+/- 0.024

• Alpha track perp. to wires• Symmetric signal (=0)


Cf-252 RunCf-252 Run preliminary







3mCi Cf-252 source3.6h live time5mg CF4 (200Torr)

no asymmetry

forward

backward


Background RunsBackground Runs• No source • Unshielded, surface run• ~1 day live time



• Cs-137 source (8Ci)• 1/3 day live time

2 events

5mg of CF4 (200Torr)

0 events


Summary and PlansSummary and Plans First observation of head-tail effect in low-energy nuclear recoils (>200keV) Work on improvements: increase gain (x2), stability of operation, lower pressure (100->50Torr) ~1m3 chamber underground within a year



Preliminary MC study

Head-tail performance with full detector


Backup




Neutronenergy

Cf-252Cf-252

Most of neutrons below threshold for alpha production (~4MeV)

Energy, angular distribution similar to DM recoils






Cross SectionsCross Sections



total

elastic

F(n,n+)N 7% of a, 17% of Nbetween 100-800keV

45% of F between 100-800keV

Predicted neutron scattering cross sections (ENDF-B/VII.0)

14.1MeV Sample dominated by elastic recoils of fluorine


F(n,n+)NF(n,n+)N



alphas



neutrons



recoils


Segment AnalysisSegment Analysis

Range: count # of pixels above threshold Measured along anode wires (+/- 3 pixels around wire) Background estimate from pixels in between wires

Energy: integral of light yield on the wire Measured in the y direction, perpendicular to anode wires In +/- 5 pixels around segment, Gaussian fit above flat

background



X projection Y projection

xy




Head-Tail with Full Detector

Head-Tail with Full Detector

• Simulation of fluorine recoils with 200GeV WIMPs



• Assumes improvements:20->60 counts/keV100->50Torr


Head-Tail ScanHead-Tail Scan



total

electronic

DT source@200TorrCf source

@200Torr

Cf/DD source<100Torr

100keV recoil angle

Source Recoil angle

14.1 MeV neutrons

80deg

Neutrons from Cf252

~57deg (avg)

200GeV WIMP

~43deg (avg)


Size of 1-Ton DetectorSize of 1-Ton Detector

1 ton of CF4 @50Torr



100 m

20 m

Gran Sasso Cavern (e.g.)

DMTPC:

16 x 16 x 16 m3

CMS: 15 x 15 x 22 m3

Super-K: 41.4m (Height) x 39.3m (Diameter)UNO: 60 ×60 ×180 m3

TAUP2007, Sendai September 13, 2007

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