1. The XENON dark matter experiment T. Shutt Princeton University

2. 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 85 Kr) Self-shielding - high density, high Z. Rich detection media –Scintillation –Ionization But: challenges remain. Scalable to large masses

3. T. Shutt TAUP 9/06/03 No. 3 WIMP LXe EdEd EsEs Dual Phase, LXe TPC PMTs - TimePrimary 5 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.

4. 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 cm 2 area 8 cm drift, 4 kV/cm Charge and light readout 128 charge readout channels 4 VUV PMTs

5. 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

6. 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

7. 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.

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

9. T. Shutt TAUP 9/06/03 No. 9 LXe Dual phase, small prototype Simple retrofit of existing chamber. Hamamatsu R6041 Primary ScintillationProportional Light (Q) EdEd EsEs PMT 207 Bi 6 cm 1 cm

10. T. Shutt TAUP 9/06/03 No. 10 Dual phase - operational parameters E s (kV/cm) % extracted Extraction from liquid Proportional scintillation Teflon structure: light collection increased by 6x

11. 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 137 Cs - 662 KeV PMT 1 PMT 2 PMT spectrum

12. T. Shutt TAUP 9/06/03 No. 12 Hamamatsu PMTs Model Photo (not same scales) Dimension & QE Radioactive Background [mBq/cm 2 ] Comment R6041 ø5 cm x 4 cm QE 5-8% 300 (Dominated by glass seal at base) Specifically designed for ops in LiqXe TPC R9288 ø5 cm x 4 cm QE 20% 7.6 (Use of Kovar for most of base) Evolution of 6041 R8520 (2.5 cm) 2 x3.5cm QE >20% 2.4 Square/quad anode- good fill factor. Columbia tested at 150K/4 atm R8778 ø5 cm x 12 cm QE 26% 1.6 (expect further improvement) Designed for XMASS. Columbia tested at 150K/4 atm

13. T. Shutt TAUP 9/06/03 No. 13 PMT activity: Monte Carlo Target 6x10 -3 /keV/kg/day Xenon between PMT and fiducial region Energy (keV) Depth (mm)

14. T. Shutt TAUP 9/06/03 No. 14 Xe purification 30 cm drift: ≈ ppt electronegative impurities (O 2, CO 2, 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

15. 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

16. 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

17. 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=10 4 –10 pF, 1 MHz: 50 e - noise. 1 atm at 160K. Gain Voltage 10 4 different pressures (Princeton) Gas Gain at Room Temperature Cryostat for two-phase tests.

18. 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 GEMs for charge readout (RICE)

19. 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 adsorption constant Rn removal system developed for Borexino

20. T. Shutt TAUP 9/06/03 No. 20 Projected XENON sensitivity 1 ton XENON projections Initial goal: 100 kG module

21. 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 207 Bi - 