the xenon dark matter experiment
DESCRIPTION
The XENON dark matter experiment. T. Shutt Princeton University. Promise of liquid Xenon. Good target (A=131) But threshold very important - 15 keV Readily purified (except 85 Kr) Self-shielding - high density, high Z. Rich detection media Scintillation Ionization - PowerPoint PPT PresentationTRANSCRIPT
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
T. Shutt TAUP 9/06/03 No. 3
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.
T. Shutt TAUP 9/06/03 No. 4
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
T. Shutt TAUP 9/06/03 No. 5
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
T. Shutt TAUP 9/06/03 No. 6
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
T. Shutt TAUP 9/06/03 No. 7
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
T. Shutt TAUP 9/06/03 No. 9
LXe
Dual phase, small prototype• Simple retrofit of existing chamber.
Hamamatsu R6041
Primary Scintillation Proportional Light (Q)
Ed
Es
PMT
207Bi6 cm
1 cm
T. Shutt TAUP 9/06/03 No. 10
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
T. Shutt TAUP 9/06/03 No. 11
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
T. Shutt TAUP 9/06/03 No. 12
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
T. Shutt TAUP 9/06/03 No. 13
PMT activity: Monte Carlo
Target 6x10-3 /keV/kg/day
Xenon between PMTand fiducial region
Energy (keV)
Dep
th (
mm
)
T. Shutt TAUP 9/06/03 No. 14
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
T. Shutt TAUP 9/06/03 No. 15
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
T. Shutt TAUP 9/06/03 No. 16
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
T. Shutt TAUP 9/06/03 No. 17
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.
T. Shutt TAUP 9/06/03 No. 18
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)
T. Shutt TAUP 9/06/03 No. 19
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
T. Shutt TAUP 9/06/03 No. 20
Projected XENON sensitivity1 ton XENON projections
Initial goal: 100 kG module
T. Shutt TAUP 9/06/03 No. 21
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 -