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					       The XENON Dark Matter Experiment
                         Elena Aprile
Physics Department and Columbia Astrophysics Laboratory
                      Columbia University

             Dark Energy 73%
Energy 2/3
     The Case for Non-Baryonic Dark Matter
              Conclusion from all Evidence

                                             WTotal = 1
                                             WL = 2/3
                                             Wm = 1/3

>95% of the Universe composition
        still unidentified.
         Ωm >> Ωb
    What is this Dark Matter?
    Non-baryonic Cold Dark Matter Candidates

Must be stable, weakly interacting and with right relic density

✦      LSP (neutralino)
✦      LKP (lightest Kaluza-Klein)
✦      Axions
✦      Solitons
✦      Wimpzillas, ..
✦                 Different mass range and interaction rate..
                      Cold Dark Matter Relics can be..

•   Produced and detected at accelerators

•   Indirectly detected via their Annihilation in
    Sun, Earth, Galaxy Neutrinos,positrons,
    antiprotons, g-rays



              …or can be directly detected in terrestrial detectors

                                  WIMP    WIMPs scatter elastically with nuclei:

                                          Rate ~ N rc/mc <sc>
                                          N = number of target nuclei in detector

                                          rc = local WIMP density

                                          <sc> = 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
Direct Detection:a challenging task
Rate: 10-1 - 10-5 /kg/day                 => Less than 1 WIMP/week will collide
Nuclear recoil energy: 10 - 100 keV       with an atom in 1kg material
Very large background: gamma rays and
neutrons from radioactivity and cosmic rays
         Detectors must effectively discriminate between
                     Nuclear Recoils (Neutrons, WIMPs)
                      Electron Recoils (gammas, betas)


WARP                           recoil

            Charge                                       Heat

                       CDMS, EDELWEISS
                  World Wide WIMP Search

   CDMS II       Majorana                                 XMASS
   CDMS I        SuperCDMS                  IGEX      KIMS
                 CLEAN                                    CsI

Boulby                                               Elegant V&VI
DRIFT                                        Gran Sasso
                                  ORPHEUS    DAMA/LIBRA
                      EDELWEISS I/II         CRESST
     CanFranc                                WARP
     IGEX                                    XENON
     ROSEBUD                                 CUORE
The XENON Experiment: Overview

                                  •   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.
       QuickTime™ and a
are needed to see this picture.   •   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 1st 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 s~2x10-45 cm2 .
              The XENON Collaboration
                    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 Shutt, Eric Dahl*, John Kwong* and Alexander Bolozdynya
                          Rice University
          Uwe Oberlack , Roman Gomez* and Peter Shagin
                          Yale University
           Daniel McKinsey, Richard Hasty, Angel Manzur*
                 Francesco Arneodo, Alfredo Ferella*
                       Coimbra University
                 Jose Matias Lopes, Joaquin Santos
                          XENON Dark Matter Goals
•XENON10 (2006-2007):
10 kg target ~2 events/10kg/month                             Dark Matter Data Plotter
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

                                                SUSY     SUSY
•XENON-1T (2008-2012?):                         Theory   Theory
1 ton (10 x 100 kg modules)                     Models   s
10-46 cm2 or ~1 event/1 tonne/month

Test majority of SUSY models.
Discover Dark Matter!
Why Liquid Xenon?
High atomic mass (A ~ 131): favorable for SI case (s ~ A2)

Odd isotope with large SD enhancement factors (129Xe, 131Xe)

High atomic number (Z=54) and density (3g/cm3)
=> 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
                  Very Typical WIMP Signal in Xe
Xe rate enhanced by high A, but low threshold necessary to avoid form factor suppression

                                           Xe Eth=16 keVr gives 0.1 event/kg/day
                                           (30% of zero thresh. sig.)
Principle of Operation
                                      WIMP or
                     nuclear          Neutron

                         Gamma or

                            Ionization & Scintillation in LXe
                                                                                  photon energy [eV]
Kubota et al. 1979, Phys. Rev.B                               7                       10                        15   20


                                                                  Kr                                       Ne

                                                         Xe                  Ar                         He

                            Xe  Xe*  2 Xe  h

                                                   200                 150                           100
                                                                             wavelength [nm]

   Xe   Xe  Xe2
                                                                        ~ 128                    LAr
   Xe2  e  Xe**  Xe            Fast     Slow

   Xe**  Xe*  heat                                                    ~ 175                LXe

   Xe  Xe*  Xe2  2 Xe  h

                                                                        ~ 77.5                   LNe
 Effect of Ionization Density on Time Dependence

A.Hitachi PRB 27 (1983)5279
                          XENON R&D Goals: Summary

+   PMTs operation in LXe                                                            Achieved
+   > 1 meter e in LXe                                                              Achieved
+   > 1 kV/cm electric field                                                         Achieved
+   dual phase operation                                                             Achieved
+   Reliable Cryogenic System                                                        Achieved
+   Nuclear recoil Scintillation Efficiency (10-55 keVr)                             Achieved
+   Nuclear recoil Ionization Efficiency                                             Achieved
+   Electron/Nuclear recoil discrimination                                           Achieved
+   Kr removal for XENON10                                Purification of 22 kg of Xe ongoing
+   Electric Field / Light Collection Simulations        Tools Developed_Done for XENON10
+   Background Simulations                               Tools Developed_Done for XENON10
+   Materials Screening for XENON10                           All major components screened
+   Assembly of XENON10 System                                                       Achieved
+   Low Activity PMTs                                                 Verified Hamamatsu #’s
+   Alternatives Readouts (SiPMs,LAAPDs,MCPs,GEMs..)                          Studies ongoing
           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
Xe-Recoils Scintillation Efficiency
       [Columbia       and Yale]                      Columbia RARAF
                                                      2.4 MeV neutrons




                                                   L ~ 20 cm

    Aprile et al., Phys. Rev. D 72 (2005)
                                                               Use pulse shape
                                            BC501A             discrimination and ToF
                                                               to identify n-recoils
                         Xe-Recoils Ionization Yield

             Energy threshold: 10 keVr

•   1st 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.

                           [Columbia, Brown and Case]
          Background discrimination capability

   ELASTIC Neutron Recoils
                    INELASTIC 131Xe
                    80 keV g + NR

                        INELASTIC 129Xe
       Neutron          40 keV g + NR
    ELASTIC Recoil             AmBe n-source       137Cs g source

5 keVee energy threshold = 10 keV nuclear recoil
       Rejection limited by edge gamma event contamination due to field irregularities

                                Teflon (PTFE)

                                                Neutron Inelastic     19F
                                                110 keV g                                electron
      Gas Xenon                       40 keV                                    recoil
      Liquid Xenon



P. Majewski                             ELASTIC Nuclear Recoil

                  improvement expected with XY position sensitive detector
               XENON3: the first 3D sensitive dual phase XeTPC

                                                                           S2 experimental value
                                                                            (# of photoelectrons)

                                                                                         Expected S2 from
                                                                                      simulation for all possible
                                                                                              x and y at
                                                                           # of PMTs    every 1x1 mm2 pixel
                                                          x and y found    (top only)
                 Hamamatsu R8520 PMT:                   at minimum chisq
        Compact metal channal: 1 inch square x 3.5 cm
           Quantum Efficiency: >20% @ 178 nm

10 cm                                                                 Fluctuation of PMT signals
                                                                        (# of pe, gain, analysis
                                                                           Uncertainties from
                                                                         (geometry, statistical)

                             10 cm
                                     a low energy event in the center,
an edge event with long drift time
                                          near LXe/GXe interface

       S1                                     S1
                                                     ~ 9 keVee

                   S2                               S2

                 σ~2 mm
                                                    σ~1 cm
Edge events can be well identified

   Pos III               Pos I

                     (Pos III)

   Pos II
                                     (Pos I)

                     (Pos II)
 XENON3: Edge events effectively removed by radial cut

                   80 keV Inelastic
                       (131Xe)                                80 keV Inelastic
                110 keV inelastic (19F)                           (131Xe)
                        + NR                                       + NR

                    40 keV Inelastic                          40 keV Inelastic
                        (129Xe)                                   (129Xe)
                         + NR                                      + NR
     Neutron                                   Neutron
   Elastic Recoil                            Elastic Recoil

XENON3’s response to neutrons (2.5 MeV from D-D generator)
                   at 1 kV/cm drift field
           XENON10: Expected Position Sensitivity from
  48 PMTs on top, 41 on bottom
8 inch diameter, 6 inch drift length
     about 15 kg liquid xenon                       Assumptions for GEANT4 Simulation

                8 inches

Top PMT Array      Bottom PMT Array, meshes, PTFE

                                                       Fitting from measurements by Columbia
                                                    and XENON Collaborators (En in keVr), see:
                                                      Aprile et al., Phys. Rev. D 72 (2005)
                                                      Aprile et al., astro-ph/0601552
                 XENON10: Expected Position Resolution

 S2 signal for each PMT from simulation,
                                                Position resolution (σ) is less than
convoluted by S2 resolution and statistical
                                              3 mm for 10 keV nuclear recoil events
  fluctuation of photoelectrons in PMTs

          10 keV nuclear recoils

                                                                               r [mm]

                                                   Position reconstruction
                                                    for XENON10: a 122
                                                   keV gamma event from
                                                         side (data)

Reconstructed positions obtained by the
 minimum chisq method (same as for
                      XENON10: Identify Multiple-step Events

                                                                              1st step
                                                     A two-step (ΔZ ~ 5 mm)
Most of the multiple scattering events                 event from XENON3
can be easily identified by drift time
separation (ΔZ > 2 mm).                                     S1           S2 2nd step

Events with ΔZ < 2 mm can be identified
by the chisq value from XY position
                                                     Simulation for XENON10




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

LNGS: March 12, 2006

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