sign: potential wimp detection using pressurized nobles

J.T. White, TAMU PPC07 May 16, 2007

SIGN:Potential WIMP Detection using

Pressurized Nobles

J.T. White

Texas A&M University

5/16/07


Why Gaseous Nobles?

• Original Motivation:– Neon

• Electron mobility possible S2/S1 discrimination fiducial well defined

• Also:– Room temperature operation

• Simpler purification• No leveling• No Cryo, etc …

• NEW!!– S2/S1 Discrimination observed !


Halo Dark Matter: Starting Assumption

ρ ~ 0.3 GeV/cc <v> ~ 250 km/s@ earth

WIMPs


WIMP Coherent Scattering (SI)

1

A

WIMP

E_recoil

20 Ascalar


A2 Dependence of Recoil Spectra

0

min

0

min22

00 )(4 v

vverf

v

vverfEF

mmvdE

dR ee

RrxeR


But, World is Radioactive!Gamma, beta

Electron recoil

U, Th, 40K, cosmogenics,etc, etc. . . .

Nuclear / Electron recoil Discrimination Very important!


S2/S1 discrimination in nobles

Gammabackground

electronrecoil

Target Nuclei

nuclear recoil

WIMP orNeutron

Scintillation

Ionization

Background Discrimination

S2

S1


Pressurized noble gasTest Cell

12.7 mm

12.7 mm

8 mm

Primary ScintillationS1

Prop. ScintillationS2

S1 S2

PTFESapphire Windows

Field Tube

Sense Wire

TPB


4-PMT - 100 atm

4-PMT Test Cell

PTFE reflector

Field tube


Sapphire Windows

TPB coating


Field Tuning

Adjust field tube potentialto optimize E-field uniformityalong sense wire


Event Waveforms (Ne-Xe example)

Neutron EventGamma Event

Areas Samei.e. ionization same

Secondary(S2)

Primary(S1)


Calibration

122 keV Gamma (+ some 136)

92 keV e-

30 keV x-ray

12.7 mm

12.7 mm

8 mmRange 92 keV e- ~ 2 mm

Xe gas: 20 atm

Range 30 keV e- ~ 0.2 mm

Range 30 keV x-ray ~ 1 cm


Calibration

122 keV Gamma

92 keV e-

30 keV x-ray

unobserved


Calibration

122 keV Gamma

92 keV e-

30 keV x-ray

Leff ~ 4.5% if Ws=76ev/phQgain ~ 1.2 p.e./e- (here)

unobserved


Neutron Scatteringw/ Mono-Energetic Neutrons

θ

Er, M

En, m

En’

Θ π

Er Ermax = (4 m M/(m+M)2) En

S – Wave

Er

dN/dErCM frame

Edge ***


4-MeV Proton Acceleratorat TAMU

Monochromatic neutrons up to 2 MeVusing 7(Li(p,n)7Be reactions.

Tandem van de Graaff

DuoplasmatronIon sourceup to ~ 15 uA

Achieved>1 uA on target >5E6 n/sr/s


Results

Xe @ 20 atm~ 300 psi


Digression: Two-Phase Xenon Discrimination

Gammas

Neutrons

Centroid Separation ~ x 2

Recoil Energy (KeVr)

S2/S1

Acceptance box

See Tom Shutt’s talk tomorrow !!

TAMU Test CellAmBe Source


Xe – 20 atm Nuclear Recoil response

S2/S1

Er_max ~ 27 keV

gammas

neutrons


S2 Spectra

Co-57 data

?


Xe – 20 atm NR Q & L yields

39 keV

27 keV Assuming Wi = 21.7 ev/e-

Assuming Leff=4.5%


Xe – S2/S1 Discrimination

23.7 116

Centroid Separation > X4

21.6 107


Results

ArXe(0.5%) @ 50 atm~ 750 psi


ArXe(0.5%) – 50 atmNR Response

Er_max ~ 104 keV

~ 15 events/ton/yr @ 10-45 pb/nEr threshold 40 keVr, Mx=100 GeV


Ar Xe(0.5%) – Charge Yield

120 keV

85 keV Average overE ~ 0.6 2.5 kV/cm

Key! (Penning effect…)


ArXe(0.5%) – Light Yield

E ~ 0.6 2.5 kV/cm E ~ 0.6 2.5 kV/cm

Key!


Results

NeXe(0.5%) @ 100 atm

1600 psi


Event Waveforms (Ne-Xe example)

Neutron EventGamma Event

Areas Samei.e. ionization same

Secondary(S2)

Primary(S1)


Nuclear Recoil Discrimination: S2 vs S1

Drift regions

Higher field

S2/S1 field (and density) dependent for nuclear recoilsGammas unaffected (Emin ~ 600 v/cm here)

Lower field

AmBe


Primary Pulse Shape Discrimination


S2/S1 AND Primary ShapeDiscrimination!

Primary Pulse Shape Discrimination

Gammas

Neutrons


NeXe(0.5%) – 100 atmNR Response

Er_max ~ 140 keV

Red = 140 keVrBased on S2

~ 1.8 evts/ton/yr @ 10-45 pb/n@ Er >= 40 keV Mx=100 GeV


NeXe(0.5%) – Q&L Yield

E ~ 0.6 2 kV/cmE ~ 0.6 2 kV/cm


SIGN conceptual design

• Gas• CsI Photocathode• Light gain structure using WLS fibers

WIMP

Primary IonizationPrompt Scintillation

Photoelectrons

Cylinder

S2 S1


Detector Concept

Composite Cylinder Hub w/ WLS Fiber structure


Drift Flow

SteeringElectrodes


Gas Light Multiplier ConceptCirlex metallized plate, ~ 1mm holes

VUV synthetic silica plates

Platinum coating – VUV transmitting

VUV -> blue phosphor coating

WLS Fibers

100% e- transmissionFluorescence E/P>1Lit – 0.006 p.e./vuv pho.


100 kg 20 atm Xe Prototype

3 m

0.6 m

Shielding

CsI

PMT

SS Tube~0.25 inch wall WLS Fibers


FutureComposite Vessels

•Carbon, Kevlar wound•Some rated > 10000 psi !•Used on mass transit (Methane))•Used for Hydrogen fuel cells•On jets, spacecraft•DOT certified !


Shielding

10 modules 1 ton

~~4-5 m

4 m watershield

See LUX discussionIn Tom Shutt’s talk


Plans – Phased Program

• 100 kg Xe proto-experiment– Water shield– SS vessel– Only 300 psi …

• Future – Neon @ 200 atm– WIMP Mass = ????– Halo velocity dispersion = ????– Number of “species” = ????

Even a caveman could do it

Xenon

Neon

sign: potential wimp detection using pressurized nobles

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