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The XENON dark matter experiment

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

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The XENON dark matter experiment

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  1. The XENON dark matter experiment T. Shutt PrincetonUniversity

  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

  3. Dual Phase, LXe TPC PMTs Background discrimination Time Background: electron recoils Recombination for nuclear recoils Es ~1 µs width Primary Signal: nuclear recoils ~40 ns width Ed LXe 5 µs/cm light charge CsI photocathode light WIMP - - - - - • 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. T. Shutt TAUP 9/06/03

  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

  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

  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

  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. T. Shutt TAUP 9/06/03

  8. 1st meeting: Nov 9, 2002 August 11, 2003

  9. Dual phase, small prototype Hamamatsu R6041 207Bi • Simple retrofit of existing chamber. PMT Es LXe Ed 1 cm 6 cm Primary Scintillation Proportional Light (Q) T. Shutt TAUP 9/06/03

  10. Dual phase - operational parameters Proportional scintillation Extraction from liquid % extracted Teflon structure: light collection increased by 6x Es (kV/cm) T. Shutt TAUP 9/06/03

  11. Single phase system 2 PMTs 3 L chamber Teflon reflector+ charge readout grids PMT spectrum 137Cs - 662 KeV PMT 2 PMT 1 • PMTs in liquid Xe • Readout • Impact on purity studied • Purity of Xe: drift length T. Shutt TAUP 9/06/03

  12. Hamamatsu PMTs T. Shutt TAUP 9/06/03

  13. PMT activity: Monte Carlo Depth (mm) Xenon between PMT and fiducial region Target 6x10-3 /keV/kg/day Energy (keV) T. Shutt TAUP 9/06/03

  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

  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

  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 T. Shutt TAUP 9/06/03

  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: G=104 • 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. T. Shutt TAUP 9/06/03

  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 • GEMs for charge readout (RICE) 63mm T. Shutt TAUP 9/06/03

  19. Removing Kr (+Ar) with chromatographic adsorption • Chromatographic separation: • Kr moves through column faster • Use He (or Ne) carrier gas Adsorption constant J.R. Michaels and N.R. Morton., 12th AEC Air Cleaning Conference, 1972. Ratio > 100 Xe Rn removal system developed for Borexino adsorption constant 195 K Kr 1/Temp T. Shutt TAUP 9/06/03

  20. Projected XENON sensitivity 1 ton XENON projections Initial goal: 100 kG module T. Shutt TAUP 9/06/03

  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 T. Shutt TAUP 9/06/03

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