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XENON10 Dark Matter Search at Case Western Reserve University

The XENON10 Collaboration at Case Western Reserve University is conducting a dark matter search using liquid xenon as the detection media. With a modular design and excellent background discrimination capabilities, the experiment shows promise for detecting WIMPs.

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XENON10 Dark Matter Search at Case Western Reserve University

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  1. The XENON10 dark matter search T. Shutt Case Western Reserve University T. Shutt, SNOLAB, 8/22/6

  2. The XENON10 Collaboration Columbia University Elena Aprile (PI), Karl-Ludwig Giboni, Sharmila Kamat, Maria Elena Monzani, , Guillaume Plante*, and Masaki Yamashita Brown University Richard Gaitskell, Simon Fiorucci, Peter Sorensen*, Luiz DeViveiros* University of Florida Laura Baudis, Jesse Angle*, Joerg Orboeck, Aaron Manalaysay* Lawrence Livermore National Laboratory Adam Bernstein, Norm Madden and Celeste Winant Case Western Reserve University Tom Shutt, Adam Bradley, Paul Brusov, Eric Dahl*, John Kwong* and Alexander Bolozdynya Rice University Uwe Oberlack , Roman Gomez* and Peter Shagin Yale University Daniel McKinsey, Richard Hasty, Angel Manzur*, Kaixuan Ni LNGS Francesco Arneodo, Alfredo Ferella* Coimbra University Jose Matias Lopes, Luis Coelho*, Joaquim Santos T. Shutt, SNOLAB, 8/22/6

  3. Promise of liquid Xenon. • Good WIMP target. • Readily purified (except 85Kr) • Self-shielding - high density, high Z. • Can separate spin, no spin isotopes 129Xe, 130Xe, 131Xe, 132Xe, 134Xe, 136Xe • ~ Low-background PMTs available • Rich detection media • Scintillation • Ionization • Recombination discriminates between electron (backgrounds) and nuclear (WIMPs, neutrons) recoils Scalable to large masses T. Shutt, SNOLAB, 8/22/6

  4. XENON: Dual Phase, LXe TPC “Calorimeter” PMTs Time Es ~1 µs Ed LXe 5 µs/cm ~40 ns - - - WIMP A. Bolozdynya, NIMA 422 p314 (1999). - • Very good 3D event location. • Background discrimination based on recombination XENON Overview • Modular design: 1 ton in ten 100 kg modules. • XENON10 Phase: 15 kg active target in Gran Sasso Lab as of March, 2006. Shield under construction. Physics runs start: June 2006. • XENON100 Phase: design/construction in FY07 and FY08 ($2M construction). Commission and undeground start physics run with 2008. T. Shutt, SNOLAB, 8/22/6

  5. Scintillation Efficiency of Nuclear Recoils Columbia and Yale Columbia RARAF 2.4 MeV neutrons p(t,3He)n Borated Polyethylene Lead LXe L ~ 20 cm  Use pulse shape discrimination and ToF to identify n-recoils BC501A Aprile et al., Phys. Rev. D 72 (2005) 072006 T. Shutt, SNOLAB, 8/22/6

  6. Nuclear and electron recoils in LXe Columbia+Brown ELASTIC Neutron Recoils INELASTIC 131Xe 80 keV  + NR Upper edge -saturation in S2 INELASTIC 129Xe 40 keV  + NR Neutron ELASTIC Recoil AmBe n-source 137Cs  source 5 keVee energy threshold = 10 keV nuclear recoil Case T. Shutt, SNOLAB, 8/22/6

  7. Charge and light yields Columbia+Brown; Case Charge yield - nuclear recoils Aprile et al., astro-ph/0601552, submitted to PRL zero field Wph-1 more zero recombination recombination less W-1 W0-1 T. Shutt, SNOLAB, 8/22/6

  8. Recombination fluctuations Case Combined energy Scintillation-based energy 40 keV (n–inelastic) Neutron Recoils • Recombination independent energy: E = W0 (ne- +ng) • Improves energy resolution • Restores linearity. • Recombination fluctuations fundamental issue for discrimination. • New energy definition itself cannot improve discrimination T. Shutt, SNOLAB, 8/22/6

  9. Discrimination at low energy Nuclear recoil data Electron recoil data (Case) Electron Recoil Band Centroid 99% Rejection (MC) Nuclear Recoil Band Centroid Nuclear Recoil Event: 5 keVr • Charge yield increase for BOTH nuclear recoils and electron recoils at low energy. • E> 20 keVr: recombination fluctuations dominate. • Monte Carlo: • >~99% discrimination at 10 keVr. This is value used in XENON10/100/1T proposals T. Shutt, SNOLAB, 8/22/6 See: T.Shutt, et al., astro-ph/0608137

  10. Some comments on Ar and Xe: atomic physics surprises • Ar: • Huge pulse-shaped discrimination needed because of 39Ar. • Very small apparent “Lindhard” factor. (Yale) • Xe scintillation discrimination: a cautionary tale LAr LAr LXe nr er • Xe: • Drop in recombination for low energy nuclear recoils • Energy independence of nuclear recoil recombination. • Drop in recombination for very low energy electron recoils

  11. “S2” signal 122 keVg (57Co) 80 keV Inelastic (131Xe) 110 keV inelastic (19F) + NR 80 keV Inelastic (131Xe) + NR Reconstructed edge events at 122 keV 40 keV Inelastic (129Xe) + NR 40 keV Inelastic (129Xe) + NR 5 mm radial cut reduces gamma events in nuclear recoils region. Neutron Elastic Recoil Resolution ≈ 2 mm. Neutron Elastic Recoil XY Position Reconstruction in 3 kg prototype Chisquare estimate from Monte Carlo - generated S2 map T. Shutt, SNOLAB, 8/22/6

  12. XENON10: Cryostat Assembly Pulse tube cryocooler Re-condenser PMTs (top 48) Gas Region LXe Active PMTs (bottom 41) Vacuum Cryostat T. Shutt, SNOLAB, 8/22/6

  13. XENON10: Detector Assembly LN Emergency Cooling Loop PMT Base (LLNL) Top PMT Array, Liquid Level Meters, HV- FT Bottom PMT Array, PTFE Vessel Grids- Tiltmeters-Case Liquid Level Meter-Yale 89 Hamamatsu R5900 (1” square) 20 cm diameter, 15 cm drift length 22 kg LXe total; 15 kg LXe active T. Shutt, SNOLAB, 8/22/6

  14. Summary: XENON10 Backgrounds Monte Carlo studies of Radioactivity (Background Events) from: • Gamma / Electron  Gammas inside Pb Shield • PMT (K/U/Th/Co) • Vessel: Stainless Steel (Co) • Contributions from Other Components  Xe Intrinsic Backgrounds (incl. 85Kr)  External Gammas - Pb Shield  Rn exclusion  Detector Performance/Design • Gamma Discrimination Requirements • Use of xyz cuts insteadof LXe Outer Veto • Neutron Backgrounds  Internal Sources: PMT (a,n)  External: Rock (a,n): Muons in Shield  Punch-through neutrons: Generated by muons in rock • NOTE: Active Muon Shield Not Required for XENON10 @ LNGS  Neutron flux from muon interaction in Pb shield << Target Level [Background Modeling U. FLORIDA / BROWN/COLUMBIA] T. Shutt, SNOLAB, 8/22/6

  15. Clearance to Crane Hook (after moving crane upwards) 20 mm XENON10 Shield Construction - LNGS Clearance Box 450 mm Clearance Box 450 mm Red-Shield DimensionBlue-Ex-LUNA Box Dimension Brown Design / LNGS Engineering 40 Tonne Pb / 3.5 Tonne Poly Low-Activity (210Pb 30 Bq/kg) inner Pb & Normal Activity (210Pb 500 Bq/kg) Outer Pb Construction Underway: Contractor COMASUD – Mid May Expect Completion of Installation LNGS (Ex-LUNA) Box Dimensions are critical constraints for shield - expansion of shield to accommodate much larger detector difficult Inner Space for XENON10 detector 900 x 900 x 1075(h) mm Crane Hook 2630 mm 2410 mm 3500 mm 200 mm 4400 mm T. Shutt, SNOLAB, 8/22/6

  16. XENON10: Punch-Through Neutron Backgrounds • High Energy Neutrons from Muons in Rock • Poly in shield is not efficient in moderating High Energy Muon-Induced Neutrons • Depth is “standard” way to reduce high energy neutron flux (LNGS effective depth is 3050 mwe) • Brown Monte Carlos show that: • Goal WIMP 1.3 evts/10 kg/mth: LNGS depth comfortably achieves goal • Goal WIMP 1.3 evts/100 kg/mth: HE Neutrons evts ~1/6 rate of dark matter. Much reduced comfort margin. (Continue to study mitigation strategies) Ratio HE Neutron BG / WIMP Signal Mei and Hime, astro-ph/0512125, calculate HE neutron/dm ~1/2–1/3 for Ge detectors at Gran Sasso Depth Additional margin could be achieved using anti-coincidence signal from muon veto (none currently in place for XENON10) around shield (c.f. CDMSII simulations indicate factor 15 reduction may be possible by tagging pions also generated in muon showers that generate HE neutrons). However, it will be important to verify that such a strategy works before relying on it. (CDMSII: Reisetter, U. Minn. / R Hennings-Yeomans, CWRU) For 2x10-46 cm2 also evaluating water/active shielding wrt all types of background T. Shutt, SNOLAB, 8/22/6

  17. Kr removal Cycle: > 1000 separation feed recovery purge Xe 10 Kg-charocoal column system at Case Kr 200 g/cycle, 2 kg/day • 85Kr - beta decay, 687 keV endpoint. • Goals for 10, 100, 1000 kg detectors: Kr/Xe < 1000, 100, 10 ppt. • Commercial Xe (SpectraGas, NJ): ~ 5 ppb (XMASS) • Chromatographic separation on charcoal column 25 Kg purifed to < 10 ppt T. Shutt, SNOLAB, 8/22/6

  18. XENON10 expected background Electron recoil background 5-25 keVee (Brown) Depth (cm) Original XENON10 Goal<0.14 /keVee/kg/day Current estimate: 2-3 x original goal Radius (cm) • Dominant background: Stainless Steel Cryostat & PMTs • Stainless Steel :100 mBq/kg 60Co • ~ 4x higher than originally assumed, but faster assembly • PMTs - 89 x 1x1” sq Hamamatsu 8520 • 17.2/<3.5/12.7/<3.9 mBq/kg, U/Th/K/Co • Increased Bg from high number of PMTs / trade off with increased position info. = Bg diagnostic • Expected background: ~ 0.4 cnts/kg/keV/day (before discr.) • Analytical estimate • Single, low-energy Compton scattering • Very forward peaked. • Probability of n scatters while traversing distance L: T. Shutt, SNOLAB, 8/22/6

  19. XENON10: Underground at LNGS T. Shutt, SNOLAB, 8/22/6

  20. XENON Box: March 7 2006 XENON Box: March 10, 2006 T. Shutt, SNOLAB, 8/22/6

  21. Test Mounting Of Detector (June 22) T. Shutt, SNOLAB, 8/22/6

  22. XENON10 Example Low Energy Event • Low Energy Compton Scattering EventS1=15.4 phe ~ 6 keVeeDrift Time ~38 μs = 76 mm(Max depth 150 mm) • Bulk gamma calib shows avg S12.3 phe/keVee0.9 phe/keVr • Trigger n>=4 in 80 ns window • Able to trigger on S1 for 10 keVr with >90% eff • Also catching S2 triggers (with pretrigger look-back) • Noise on separate PMT chans <<0.1 phe equiv T. Shutt, SNOLAB, 8/22/6

  23. Status of XENON10 CDMS II goal Dark Matter Data Plotterhttp://dmtools.brown.edu SUSY TheoryModels • 15 kg detector (~8 kg fiducial) now operational in Gran Sasso • First low background operations in shield started 8/12. • Calibrations ongoing • Activated Xe soon • 164 + 236 keV lines • 80 keV beta. • Neutron • External gammas • Background close to expectation • Results soon. SUSY TheoryModels T. Shutt, SNOLAB, 8/22/6

  24. Scaling LXe Detector: Fiducial BG Reduction /1 • Compare LXe Detectors (factor 2 linear scale up each time)15 kg (ø21 cm x 15 cm) -> 118 kg (ø42 cm x 30 cm) -> 1041 kg (ø84 cm x 60 cm) • Monte Carlos simply assume external activity scales with area (from PMTs and cryostat) using XENON10 values from screening Low energy rate in FV before any ER vs NR rejection /keVee/kg/day Gross Mass 15 kg 118 kg 1041 kg x2 linear x2 linear x10 reduction >102 reduction (Brown) Fiducial Mass T. Shutt, SNOLAB, 8/22/6 dru = cts/keVee/kg/day

  25. Scaling LXe Detector: Fiducial BG Reduction /2 • Assuming ER are rejected at 99% for 50% acceptance of NR • Diagonal dashed lines show background x exposure giving 1 event leakage • If rej. 99% -> 99.5% and acc. 50% -> ~100% then all σ are better by 4x Low energy rate in FV before any ER vs NR rejection /keVee/kg/day Gross Mass 15 kg 118 kg 1041 kg x2 linear x2 linear σ = 4 10-43 cm2 XENON10 - 400 mdruee7 live-days x 8 kg fid x10 reduction 1 leakage event (rej 99%) σ = 4 10-44 cm2 “118 kg” - 40 mdruee30 live-days x 20 kg fid >102 reduction 1 week 1 month σ = 2 10-46 cm2 “1041 kg” - 0.2 mdruee1200 live-days x 100 kg fid 1 year 4 years Reference: Current CDMS II 90% CL σ = 2 10-43 cm2 for 100 GeV WIMP Fiducial Mass (Brown) T. Shutt, SNOLAB, 8/22/6 dru = cts/keVee/kg/day

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