1. The XENON Dark Matter Experiment Elena Aprile Physics Department and Columbia Astrophysics Laboratory Columbia University http://www.astro.columbia.edu/~lxe/XENON/

2. Energy 2/3 Dark Energy 73%

3. The Case for Non-Baryonic Dark Matter Conclusion from all Evidence  Total = 1   = 2/3  m = 1/3 >95% of the Universe composition still unidentified. Ω m >> Ω b What is this Dark Matter?

4. Non-baryonic Cold Dark Matter Candidates ✦ LSP (neutralino) ✦ LKP (lightest Kaluza-Klein) ✦ Axions ✦ Solitons ✦ Wimpzillas,.. ✦ Different mass range and interaction rate.. Must be stable, weakly interacting and with right relic density WIMPs

5. ANTARES LHC Cold Dark Matter Relics can be.. Produced and detected at accelerators Indirectly detected via their Annihilation in Sun, Earth, Galaxy  Neutrinos,positrons, antiprotons,  -rays GLAST AMS AMANDA/ICECUBE

6. … or can be directly detected in terrestrial detectors WIMPs scatter elastically with nuclei: Rate ~ N    m  N = number of target nuclei in detector   = local WIMP density = scattering cross section From the density of dark matter in the galaxy: Every liter of space: 10-100 WIMPs, moving at 1/1000 the speed of light => Less than 1 WIMP/week will collide with an atom in 1kg material WIMP Direct Detection:a challenging task Rate: 10 -1 - 10 -5 /kg/day Nuclear recoil energy: 10 - 100 keV Very large background: gamma rays and neutrons from radioactivity and cosmic rays

7. Detectors must effectively discriminate between Nuclear Recoils (Neutrons, WIMPs) Electron Recoils (gammas, betas) recoil energy Light Charge Heat CDMS, EDELWEISS CRESST ZEPLIN XMASS XENON WARP

8. World Wide WIMP Search Picasso CDMS I LiF Elegant V&VI CsI IGEX Gran Sasso DAMA/LIBRA CRESST WARP XENON CUORE CanFranc IGEX ROSEBUD ANAIS ArDM EDELWEISS I/II Boulby ZEPLIN I/II/III/MAX DRIFT x XMASS KIMS Majorana SuperCDMS CLEAN ORPHEUS CDMS II

9. Modular design: 1 ton active Xe distributed in an array of ten 3D position sensitive dual-phase (liquid/gas) XeTPCs, actively shielded by a LXe veto. Simultaneous detection of ionization and scintillation for event-by-event discrimination of nuclear recoils from electron recoils (>99.5%) down to 16 keVr. XENON funded by NSF and DOE. Phase1 (XENON10) : 15 kg detector has been installed in Gran Sasso Lab ( equipment arrived on March 7, 2006). Shield construction to be completed by May 15, 2006. XENON10 physics run (June-Aug, 2006) will determine design of 1 st 100 kg module Phase2 (XENON100): Goal is data taking by late 2007. After 3 months at a background < 1x10 -4 cts/keV/kg/day after rejection, the sensitivity of XENON100 would be  ~2x10 -45 cm 2. The XENON Experiment: Overview

10. Columbia University Elena Aprile (PI), Karl-Ludwig Giboni, Sharmila Kamat, Maria Elena Monzani, Kaixuan Ni*, 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, Chris Hagmann, Norm Madden and Celeste Winant Case Western Reserve University Tom Shut t, Eric Dahl*, John Kwong* and Alexander Bolozdynya Rice University Uwe Oberlack, Roman Gomez* and Peter Shagin Yale University Daniel McKinsey, Richard Hasty, Angel Manzur* LNGS Francesco Arneodo, Alfredo Ferella* Coimbra University Jose Matias Lopes, Joaquin Santos The XENON Collaboration

11. XENON Dark Matter Goals SUSY Theory Models Dark Matter Data Plotter http://dmtools.brown.edu http://dmtools.brown.edu CDMS II goal SUSY Theory Model s XENON10 (2006-2007): 10 kg target ~2 events/10kg/month Equivalent CDMSII Goal for mass >100 GeV (Current CDMS limit is 10 x above this level) Important goal of XENON10 underground is to establish performance of dual phase TPC to design optimized XENON100 XENON100 (2007-2008): 100 kg target ~2 events/100kg/month XENON-1T (2008-2012?): 1 ton (10 x 100 kg modules) 10 -46 cm 2 or ~1 event/1 tonne/month Test majority of SUSY models. Discover Dark Matter!

12. Why Liquid Xenon? High atomic mass (A ~ 131): favorable for SI case (  ~ A 2 ) Odd isotope with large SD enhancement factors ( 129 Xe, 131 Xe) High atomic number (Z=54) and density (3g/cm 3 ) => compact, self-shielding geometry ‘Easy’ cryogenics at -100 C No long-lived radioisotopes Excellent Scintillator (~NaI(Tl)) and Efficient Ionizer (W=15.6 eV) Simultaneous Light and Charge Detection => background discrimination

13. Xe E th =16 keVr gives 0.1 event/kg/day (30% of zero thresh. sig.) Very Typical WIMP Signal in Xe Xe rate enhanced by high A, but low threshold necessary to avoid form factor suppression

14. Principle of Operation WIMP or Neutron nuclear recoil electron recoil Gamma or Electron

15. FastSlow Kubota et al. 1979, Phys. Rev.B Ionization & Scintillation in LXe

16. Fig.14 Scintillation Decay Curves Liq. Ar

17. Effect of Ionization Density on Time Dependence A.Hitachi PRB 27 (1983)5279

18. XENON R&D Goals: Summary + PMTs operation in LXe + > 1 meter  in LXe + > 1 kV/cm electric field + dual phase operation + Reliable Cryogenic System + Nuclear recoil Scintillation Efficiency (10-55 keVr) + Nuclear recoil Ionization Efficiency + Electron/Nuclear recoil discrimination + Kr removal for XENON10 + Electric Field / Light Collection Simulations + Background Simulations + Materials Screening for XENON10 + Assembly of XENON10 System + Low Activity PMTs + Alternatives Readouts (SiPMs,LAAPDs,MCPs,GEMs..) Achieved Achieved Purification of 22 kg of Xe ongoing Tools Developed_Done for XENON10 All major components screened Achieved Verified Hamamatsu #’s Studies ongoing

19. Recent Highlights from XENON R&D LXe Scintillation Efficiency for Nuclear Recoils  The most important parameter for DM search  No prior measurement at low energies Aprile at al., Phys. Rev. D 72 (2005) 072006 LXe Ionization Efficiency for Nuclear Recoils  XENON concept based on simultaneous detection of recoil ionization and scintillation  No prior information on the ionization yield as a function of energy and applied E- field Aprile et al., PRL (2006), astro-ph/0601552 Development of XENON10 Experiment for Underground Deployment  Validated Cryogenics, HV, DAQ systems with 6kg prototype (XENON3)  Demonstrated low energy threshold and 3D position reconstruction  Installed/tested larger (15 kg) detector in same cryostat (Dec 05- Feb06)  XENON10 equipment shipped to Italy on March 2, 2006

20. Xe-Recoils Scintillation Efficiency p(t, 3 He)n Borated Polyethylene Lead LXe L ~ 20 cm  BC501A Use pulse shape discrimination and ToF to identify n-recoils Columbia RARAF 2.4 MeV neutrons Aprile et al., Phys. Rev. D 72 (2005) [ Columbia and Yale]

21. Xe-Recoils Ionization Yield 1 st Measurement of the charge of low energy recoils in LXe and of the field dependence. Charge yield surprisingly higher than expected and with very weak field dependence. Energy threshold: 10 keVr [Columbia, Brown and Case]

22. ELASTIC Neutron Recoils INELASTIC 129Xe 40 keV  + NR INELASTIC 131Xe 80 keV  + NR 137Cs  source Upper edge -saturation in S2 AmBe n-source Neutron ELASTIC Recoil 5 keVee energy threshold = 10 keV nuclear recoil Background discrimination capability

23. Rejection limited by edge gamma event contamination due to field irregularities nuclear recoil electron recoil improvement expected with XY position sensitive detector

24. XENON3: the first 3D sensitive dual phase XeTPC 10 cm Hamamatsu R8520 PMT: Compact metal channal: 1 inch square x 3.5 cm Quantum Efficiency: >20% @ 178 nm 10 cm x and y found at minimum chisq # of PMTs (top only) S2 experimental value (# of photoelectrons) Expected S2 from simulation for all possible x and y at every 1x1 mm 2 pixel Fluctuation of PMT signals (# of pe, gain, analysis error) + Uncertainties from simulation (geometry, statistical)

25. a low energy event in the center, near LXe/GXe interface S2 S1 ~ 9 keVee σ~1 cm an edge event with long drift time S2 S1 σ~2 mm

26. Edge events can be well identified Pos III Co-57 (Pos I) Co-57 (Pos III) Co-57 (Pos II) Pos II Pos I

27. XENON3: Edge events effectively removed by radial cut XENON3’s response to neutrons (2.5 MeV from D-D generator) at 1 kV/cm drift field Neutron Elastic Recoil 40 keV Inelastic ( 129 Xe) + NR 80 keV Inelastic ( 131 Xe) 110 keV inelastic ( 19 F) + NR Neutron Elastic Recoil 40 keV Inelastic ( 129 Xe) + NR 80 keV Inelastic ( 131 Xe) + NR

28. XENON10: Expected Position Sensitivity from Simulation Assumptions for GEANT4 Simulation 48 PMTs on top, 41 on bottom 8 inch diameter, 6 inch drift length about 15 kg liquid xenon 8 inches Fitting from measurements by Columbia and XENON Collaborators (E n in keVr), see: Aprile et al., Phys. Rev. D 72 (2005) 072006 Aprile et al., astro-ph/0601552 Top PMT ArrayBottom PMT Array, meshes, PTFE

29. 10 keV nuclear recoils XENON10: Expected Position Resolution S2 signal for each PMT from simulation, convoluted by S2 resolution and statistical fluctuation of photoelectrons in PMTs Reconstructed positions obtained by the minimum chisq method (same as for XENON3) Position reconstruction for XENON10: a 122 keV gamma event from side (data) r [mm] Position resolution (σ) is less than 3 mm for 10 keV nuclear recoil events

30. XENON10: Identify Multiple-step Events One neutron event with two steps (5 keVr each) separated by ΔL Events with two steps separated by more than 3 cm in XY can be efficiently identified. ΔL Simulation for XENON10 n n LXe Events with ΔZ < 2 mm can be identified by the chisq value from XY position reconstruction. Most of the multiple scattering events can be easily identified by drift time separation (ΔZ > 2 mm). A two-step ( ΔZ ~ 5 mm) event from XENON3 S1S2 1st step 2nd step

31. Tested all systems prior to shipping to LNGS 48 PMTs on top, 41 on bottom, 20 cm diameter, 15 cm drift length 22 kg of Xe to fill the TPC. Active volume ~15 kg. XENON10 TPC at Columbia Nevis Laboratory

32. XENON10 at Gran Sasso National Laboratory XENON10 Shield Construction started in XENON Box ( ex-LUNA) Testing/Calibrating unshielded XENON10 (March-April 06) in neighboring Box

33. LNGS: March 12, 2006