The XENON dark matter experiment

1
The XENON dark matter experiment

• T. Shutt
• Princeton University

2
Promise of liquid Xenon.

• Good target (A131)
• 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
3
Dual Phase, LXe TPC

• Need single charge, photon sensitivity
• Use charge amplification at high field instead of
  increasing ?E/kT.
• Despite small number of e-, g, discrimination
  still good.

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

5
XENON history

• Proposed as RD project to NSF in Sept. 2001
• SAGENAP, Feb 2001
• Funded Sept 2002.
• First year now complete.
• This next year fully functioning, multi- kG
  module

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
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.

8
1st meeting Nov 9, 2002
August 11, 2003
9
Dual phase, small prototype

• Simple retrofit of existing chamber.

PMT
Es
LXe
Ed
1 cm
6 cm
Primary Scintillation
Proportional Light (Q)
10
Dual phase - operational parameters
11
Single phase system

• PMTs in liquid Xe
• Readout
• Impact on purity studied
• Purity of Xe drift length

12
Hamamatsu PMTs
Model Photo(not same scales) Dimension QE Radioactive BackgroundmBq/cm2 Comment
R6041 ø5 cm x 4 cmQE 5-8 300(Dominated by glass seal at base) Specifically designed for ops in LiqXe TPC
R9288 ø5 cm x 4 cmQE 20 7.6(Use of Kovar for most of base) Evolution of 6041
R8520 (2.5 cm)2x3.5cmQE gt20 2.4 Square/quad anode-good fill factor. Columbia tested at 150K/4 atm
R8778 ø5 cm x 12 cmQE 26 1.6(expect further improvement) Designed for XMASS. Columbia tested at 150K/4 atm
13
PMT activity Monte Carlo
Depth (mm)
Xenon between PMT and fiducial region
Target 6x10-3 /keV/kg/day
Energy (keV)
14
Xe purification

• 30 cm drift ppt electronegative impurities
  (O2, CO2, NO, etc.)
• Xe difficult compared to Ar.
• Polarizability -gt 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
15
Multi-kg prototype

• 7 PMTs in gas.
• Can fit any of PMTs discussed
• 13 cm Ø active area, gt 10 cm drift length
• Pulse Tube Refrigerator with T control
• Interior materials low background, cryostat not.

Cryostat design
Sept. '03
16
Multi-Kg prototype

• Light collection goal 1 PE/keV
• Need top/bottom light collection
• CsI photocathode
• Bottom set of PMTs

Simulated light collection
Chamber interior design
17
MWPC charge readout
(Princeton)

• Eliminates PMTs
• Light CsI photocathode.
• Challenge limited gain with no quench gas.
• Single electron measurement possible with wires
• New measurement G104
• 10 pF, 1 MHz 50 e- noise.

Gas Gain at Room Temperature
Gain
1 atm at 160K.
different pressures
104
Voltage
Cryostat for two-phase tests.
18
Advanced readout schemes

• Burle MCP-based PMTs (Brown)
• QE -gt 30
• U/Th/K 400 mBq
• Tested to 77K at 1 atm
• Good for tiling
• Separate anodes for position resolution

• GEMs for charge readout (RICE)

63mm
19
Removing Kr (Ar) with chromatographic adsorption
Adsorption constant

• Chromatographic separation
• Kr moves through column faster
• Use He (or Ne) carrier gas

J.R. Michaels and N.R. Morton., 12th AEC Air
Cleaning Conference, 1972.
Ratio gt 100
Xe
Rn removal system developed for Borexino
adsorption constant
195 K
Kr
1/Temp
20
Projected XENON sensitivity
1 ton XENON projections

• Initial goal 100 kG module

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 - b, g