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XENON Dark Matter Project

XENON Dark Matter Project. Karen Chen Boston College Nevis Labs, Columbia REU 2009. Outline. I: Xenon Detector Concepts ER and NR Discrimination II: Previous Work XENON100 III: Current Work XENON100 Upgrade. Xenon Detector Concept. Xe Dual phase TPC

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XENON Dark Matter Project

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  1. XENON Dark Matter Project Karen Chen Boston College Nevis Labs, Columbia REU 2009

  2. Outline • I: Xenon Detector Concepts • ER and NR Discrimination • II: Previous Work • XENON100 • III: Current Work • XENON100 Upgrade

  3. Xenon Detector Concept Xe Dual phase TPC • Evidence of non-baryonic dark matter • WIMPs • Elastic collisions anode cathode

  4. Xenon Detector Concept • Interaction • (S1) Light • e- drift • Proportional scintillation • (S2) Light anode cathode

  5. ER and NR Sources • Nuclear recoils (NR) • Neutrons • Created from cosmic muons • (alpha,n) • WIMPs • Electronic recoils (ER) • Gamma and beta rays • construction materials cathode anode

  6. ER and NR Sources • Maximize WIMP events • Large detector size • Minimize Background • Low radioactivity materials • Shielding • Underground laboratory (LNGS)

  7. XENON Detectors Past, Present, and Future • XENON10 (2005-2007) • Demonstrated dual phase xenon TPC for WIMP search • XENON100 (2006-2009) • 50kg fiducial volume (FV) mass • Simulation and Experimental results • XENON100+ (2009-2012) • 100kg FV • Under current R&D (that’s me!) • Detector Geometry • Background simulations • Based on XENON100 data • XENON1T (2013-2015) • 1 ton FV • Early R&D

  8. XENON100 • Screen materials for radioactivity • 238U, 232Th, 40K, and 60Co • Ge detector • Vary by manufacturer and thickness Measured radiation rates for materials in XENON100 (plus QUPIDS)

  9. XENON100 • How many bananas is that? • PMTs and bases – 4.2 Bq • Stainless steel – 4.1 Bq • PTFE – 0.1 Bq • Total – 8.4 Bq • Banana* ~ 20 Bq, ~2x • Human** ~ 4000 Bq, ~476x **Wikipedia *http://www.radlab.nl/radsafe/archives/9503/msg00074.html

  10. XENON100 • Background rate for different materials MC Simulation by Alex

  11. PMTs and QUPIDs • Primary BG source • Photomultiplier tubes (PMTs) • Lowest radioactivity on the market! • Need lower radioactivity PMTs! • Quartz Photon Intensifying Detector (QUPID) • Developed by Hamamatsu Photonics and Prof. Arisaka (UCLA)

  12. PMTs and QUPIDs XENON10 and XENON100 • 98 top PMTs with ~24% QE • 80 bottom PMTs with ~34% QE XENON100+ and XENON1T • Same top array • 19 bottom QUPIDs • $$$ QUPIDs created for XENON100 Upgrade

  13. XENON100 Upgrade Improvements on XENON100 • Reducing Background • Lower radioactivity materials • QUPIDs • More Xe, less material • Cryostat - Domed for stability • Steel thickness from 1.5mm to 0.1mm • Need to test • Exception: • More can be better Shielding Scaling Up Add radius or height?

  14. XENON100 Upgrade • Steel vs Copper Cryostat • Copper • High thermal conductivity • Soft Metal • Low BG • Stainless Steel • Medium thermal conductivity • Sturdy • High BG MC Simulation by Alex

  15. XENON100 Upgrade • Copper • High thermal conductivity • Soft Metal • Low BG • Stainless Steel • Medium thermal conductivity • Sturdy • High BG LXe 170K

  16. Shielding • Separate the xenon • Cooling tower moved for Xenon100 • The trade off: • Less external BG • neutrons, muons • More intrinsic BG • radioactive decay • Cutting Costs: • XENON1T Shield Shielding for Xenon100 Upgrade

  17. XENON100 Upgrade • Detector Geometry • Double the mass • Height or radius? • Radius limited by QUPIDs • Increase the height • height  drift length • Drift Length Concerns • High voltage • Pileup Problem QUPIDs

  18. Pileup Problem • What is pileup? • Events recorded by trigger • Noise or signal? • Record length • Time for electron to drift from one end to the other • S1 and S2 signal in one event • Multiple events -> Uncertainty

  19. Pileup Problem • Event A S1 Signal • Electron A drifts • Event B S1 Signal • Electrons drift • Event B S2 Signal • Event A S2 Signal • Which signal corresponds to which event? Detector

  20. Pileup Problem Estimate likelihood of pileup n =true interaction rate m =recorded count rate τ = dead time (record length) m = ne-nτ* Percent Loss = 1 - e-nτ • But what is the trigger rate? *Radiation Detection and Measurement by Knoll pgs 120-123

  21. XENON100 Upgrade • Ideas into Monte Carlo Simulations • If I use this geometry, what BG can I expect? • Geant4 • Create the detector geometry • XENON100 • Simplified: Bell, Cryostat, PMTs, Teflon panel Simulate the decay chains 238U, 232Th, 40K, 60Co Scale by radioactivity of each material Analyze - Make appropriate cuts Multiple scatters, energy Fiducial volume

  22. XENON100 Upgrade Steel Cryostat (Inner) Bell Steel Cryostat (Inner) PMTs Teflon Teflon Panel QUPIDs TPC/Target Xe Veto

  23. XENON100 Upgrade • Ideas into Monte Carlo Simulations • If I use this geometry, what BG can I expect? • Geant4 • Create the detector geometry • XENON100 • Simplified: Bell, Cryostat, PMTs, Teflon panel • Simulate the decay chains • 238U, 232Th, 40K, 60Co • Scale by radioactivity of each material Analyze - Make appropriate cuts Multiple scatters, energy Fiducial volume

  24. XENON100 Upgrade • Simulation check: • Rates scale with mass XENON100 (Alex) XENON100 Upgrade (Karen)

  25. XENON100 Upgrade • Side note: • Manipulating energy spectrum with thickness K40 U238 Th232 Co60 K40 U238 Th232 Co60

  26. XENON100 Upgrade • Side note: • Material thickness and K-40 spectrum

  27. XENON100 Upgrade • Event Rate and Energy All Materials PMTs Steel Teflon Copper Trigger rate estimate: ~0.05Hz

  28. XENON100 Upgrade • Ideas into Monte Carlo Simulations • If I use this geometry, what BG can I expect? • Geant4 • Create the detector geometry • XENON100 • Simplified: Bell, Cryostat, PMTs, Teflon panel • Simulate the decay chains • 238U, 232Th, 40K, 60Co • Scale by radioactivity of each material • Analyze - Make appropriate cuts • Multiple scatters, energy • Fiducial volume

  29. XENON100 Upgrade • Number of scatters • Detector Resolution • ~3mm • Single scatter events in the target volume • Good efficiency from PMTs • Events in the xenon veto • Low efficiency of veto PMTs • need >50keVee of energy

  30. XENON100 Upgrade • Different energy in veto cuts

  31. XENON100 Upgrade • Different energy in veto cuts • Histogram of events in the best volume cut

  32. XENON100 Upgrade Xenon100 Event distribution (Alex) • Event Distribution • Fiducial Volume Cut • Low background core • Radial vs Height cuts

  33. XENON100 Upgrade • Event Distribution: PMTs

  34. XENON100 Upgrade • Event Distribution: Steel

  35. XENON100 Upgrade • Event Distribution: Teflon

  36. XENON100 Upgrade • Event Distribution: Copper

  37. XENON100 Upgrade • Event Distribution: All

  38. XENON100 Upgrade • Event Distribution Patterns • Top Heavy: Steel and PMTs • Radial: Teflon, Steel (somewhat) Radial cut - - - - - - - - - - - - > Height cut

  39. XENON100 Upgrade • Added Top Xenon Veto Xe Top Veto Xe Veto

  40. XENON100 Upgrade • Current Design and BG rate • Steel contribution is lowered! • Looks promising! • Reached low background rates in proposal • Doubled FV

  41. Summary • XENON100 • BG contribution from different materials • XENON100 upgrade • Steel vs Copper cryostat • Doubling the mass -> height ->drift length • Pileup – not an issue • Ideas for detector geometry • Analyzed MC simulation results • Effect of veto energy cut • Background levels, trigger rate • Re-simulated with top LXe veto -> Steel BG • BG levels within design levels in NSF proposal

  42. Acknowledgements • XENON Group • Rafael • Elena Aprile • Guillame, Bin, Kyungeun (Elizabeth), Luke • Emily • Nevis REU • Mike Shaevitz, John Parsons • All my fellow REU students

  43. Questions? • XENON100 • BG contribution from different materials • XENON100 upgrade • Steel vs Copper cryostat • Doubling the mass -> height ->drift length • Pileup – not an issue • Analyzed MC simulation results • Effect of veto energy cut • Background levels, trigger rate • Re-simulated with top LXe veto • BG levels within design levels in NSF proposal

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