The XENON dark matter experiment T. Shutt Princeton University

The XENON dark matter experiment

T. Shutt

Princeton University

T. Shutt TAUP 9/06/03 No. 2

Promise of liquid Xenon.• Good target (A=131)

– But threshold very important - 15 keV

• Readily purified (except 85Kr)

• Self-shielding - high density, high Z.

• Rich detection media– Scintillation– Ionization

• But: challenges remain.

Scalable to large masses


WIMP

LXe Ed

Es

Dual Phase, LXe TPC

PMTs

-

TimeTime

PrimaryPrimary5 µs/cm

~40 ns width

~1 µs width

---

CsI photocathode

-• Need single charge, photon sensitivity

– Use charge amplification at high field instead of increasing ∆E/kT.

• Despite small number of e-, , discrimination still good.

light

Background:electron recoils

Signal: nuclear recoils

charge

light

Recombination for nuclear recoils

Background discrimination

B.A.Dolgoshein, V.N. Lebedenko, B.U. Rodionov, JETP Lett. 11 (1970) 513.


Prototype "0": Columbia LXe TPC

• LXEGrit balloon-borne gamma-ray telescope

• 30 kg active Xe mass• 20x20 cm2 area• 8 cm drift, 4 kV/cm• Charge and light readout• 128 charge readout channels• 4 VUV PMTs


XENON history• Proposed as R&D project to NSF in Sept. 2001

– SAGENAP, Feb 2001

• Funded Sept 2002.

• First year now complete.

• This next year: fully functioning, multi- kG module


The XENON Collaboration

Columbia University Elena Aprile (PI), Edward Baltz ,Karl-Ludwig Giboni ,Chuck Hailey ,Lam

Hui Masanori Kobayashi ,Pawel Majewski ,Kaixuan Ni Rice University

Uwe Oberlack ,Omar Vargas Princeton University

John Kwong, Tom Hartmann, Kirk McDonald, Nathaniel Ross, Tom Shutt

Brown University Richard Gaitskell, Peter Sorensen, Luiz DeViveiros

Lawrence Livermore National Laboratory William Craig

Stockholm University, Sweden Vladimir Peskov


A busy year• Dual phase, 1 cm drift• Single phase, charge + PMTs in liquid.• PMT studies• Purity• New chambers: Princeton, Rice• MCP PMTs• Charge readout with MWPC• GEMs• Kr removal• Multi-Kg prototype:

– Construction of cryostat. – Design of chamber underway.

1st meeting: Nov 9, 2002

August 11, 2003


LXe

Dual phase, small prototype• Simple retrofit of existing chamber.

Hamamatsu R6041

Primary Scintillation Proportional Light (Q)

Ed

Es

PMT

207Bi6 cm

1 cm


Dual phase - operational parameters

50

60

70

80

90

100

110

1.5 2 2.5 3 3.5 4 4.5 5 5.5

570 keV gamma rays 05/22/03

1 kV/cm

1.5 kV/cm

2 kV/cm

2.5 kV/cm

3 kV/cm

Corrected Charge %

Extraction Field

Es (kV/cm)

% e

xtra

cted

Extraction from liquid

Proportional scintillation

Teflon structure:light collectionincreased by 6x


Single phase system

• PMTs in liquid Xe– Readout

– Impact on purity studied

• Purity of Xe: drift length

2 PMTs

3 L chamber Teflon reflector+ charge readout grids

137Cs - 662 KeV

PMT 1

PM

T 2

PMT spectrum

http://www.astro.columbia.edu/~lxe/XENON/internal/newsys/dsc00854.jpg


Hamamatsu PMTs

ModelPhoto

(not same scales)Dimension

& QE

Radioactive Background[mBq/cm2]

Comment

R6041ø5 cm x 4 cm

QE 5-8%

300(Dominated by

glass seal at base)

Specifically designed for ops in

LiqXe TPC

R9288ø5 cm x 4 cm

QE 20%

7.6(Use of Kovar

for most of base)Evolution of 6041

R8520(2.5 cm)2x3.5cm

QE >20%2.4

Square/quad anode-good fill factor.

Columbia tested at 150K/4 atm

R8778ø5 cm x 12 cm

QE 26%

1.6(expect further improvement)

Designed for XMASS. Columbia

tested at 150K/4 atm


PMT activity: Monte Carlo

Target 6x10-3 /keV/kg/day

Xenon between PMTand fiducial region

Energy (keV)

Dep

th (

mm

)


Xe purification

• 30 cm drift: ≈ ppt electronegative impurities (O2, CO2, NO, etc.)

– Xe difficult compared to Ar. • Polarizability -> Vanderwaals forces: high

solubility for contaminats

• 160 K not that cold

• Established gas purification techniques - gettering, spark gap purification

• Chamber: UHV techniques. Materials selection, cleaning, baking.

Gas system suitable for 100 kg Xe


Multi-kg prototype• 7 PMTs in gas.

– Can fit any of PMTs discussed

• 13 cm Ø active area, > 10 cm drift length

• Pulse Tube Refrigerator with T control• Interior materials low background,

cryostat not.

Cryostat design

Sept. '03


Multi-Kg prototype

Simulated light collection

Chamber interior design

• Light collection goal: 1 PE/keV• Need top/bottom light collection

– CsI photocathode

– Bottom set of PMTs


MWPC charge readout • Eliminates PMTs

– Light: CsI photocathode.

• Challenge: limited gain with no quench gas.

• Single electron measurement possible with wires– New measurement: G=104

– 10 pF, 1 MHz: 50 e- noise.

1 atm at 160K.Gai

nVoltage

104

different pressures

(Princeton)

Gas Gain at Room Temperature

Cryostat for two-phase tests.


Advanced readout schemes• Burle MCP-based PMTs

(Brown)– QE -> 30%– U/Th/K ~ 400 mBq– Tested to 77K at 1 atm– Good for tiling– Separate anodes for position

resolution

63mm

QuickTime™ and aTIFF (LZW) decompressorare needed to see this picture.

• GEMs for charge readout (RICE)


Removing Kr (+Ar) with chromatographic adsorption

J.R. Michaels and N.R. Morton.,12th AEC Air Cleaning Conference, 1972.

195 K

Adsorption constant

Ratio > 100

• Chromatographic separation:– Kr moves through column faster

– Use He (or Ne) carrier gas

Xe

Kr

1/Temp

adso

rpti

on c

onst

ant

Rn removal system developed for Borexino


Projected XENON sensitivity1 ton XENON projections

Initial goal: 100 kG module


XENON to absorb• Dual phase, 1 cm drift setup

– Cold PMT implemented

– 2 phase detection working

– Next: Teflon reflector.

• ≈ 10 cm drift length measurements – Demonstration of good electron drift

with Teflon

• Setups at Brown, Princeton, Rice

• Design of 10 kg prototype underway– 7 PMTs

– Pulse-tube cryostat

• 100 kg module goal

207Bi -

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The XENON dark matter experiment T. Shutt Princeton University