The XENON Dark Matter Experiment

Elena Aprile

Physics Department and Columbia Astrophysics Laboratory

Columbia University

http://www.astro.columbia.edu/~lxe/XENON/

Energy 2/3

Dark Energy 73%

The Case for Non-Baryonic Dark MatterConclusion from all Evidence

Total = 1 = 2/3m = 1/3

>95% of the Universe composition still unidentified.

ΩΩmm >> Ω >> ΩbbWhat is this Dark Matter?

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

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

GLASTAMS

AMANDA/ICECUBE

…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

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

Detectors must effectively discriminate between Nuclear Recoils (Neutrons, WIMPs) Electron Recoils (gammas, betas)

recoil energy

Light

Charge Heat

CDMS, EDELWEISS

CRESSTZEPLINXMASSXENONWARP

World Wide WIMP Search

Picasso

CDMS I

LiFElegant V&VI

CsI

IGEX

Gran SassoDAMA/LIBRACRESST WARPXENONCUORE

CanFrancIGEXROSEBUDANAISArDM

EDELWEISS I/II

BoulbyZEPLIN I/II/III/MAXDRIFT

x XMASSKIMS

MajoranaSuperCDMSCLEAN

ORPHEUS

CDMS II

• 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 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 ~2x10-45 cm2 .

The XENON Experiment: Overview

QuickTime™ and a decompressor

are needed to see this picture.

Columbia University Elena Aprile (PI), Karl-Ludwig Giboni, Sharmila Kamat,

Maria Elena Monzani, Kaixuan Ni*, Guillaume Plante*, and Masaki YamashitaBrown 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 WinantCase Western Reserve University

Tom Shutt, Eric Dahl*, John Kwong* and Alexander BolozdynyaRice University

Uwe Oberlack , Roman Gomez* and Peter ShaginYale University

Daniel McKinsey, Richard Hasty, Angel Manzur*LNGS

Francesco Arneodo, Alfredo Ferella*Coimbra University

Jose Matias Lopes, Joaquin Santos

The XENON Collaboration

XENON Dark Matter Goals

SUSY TheoryModels

Dark Matter Data Plotterhttp://dmtools.brown.edu

CDMS II goal

SUSY TheoryModels

•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 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 ( ~ 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

Xe Eth=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

Principle of OperationWIMP or Neutronnuclear

recoil

electronrecoil

Gamma or Electron

Fast Slow

Kubota et al. 1979, Phys. Rev.B

Ionization & Scintillation in LXe

.

7 10 15 20

photon energy [eV]

200 150 100

wavelength [nm]

liquid

solid

gas

Kr Ne

Xe Ar He

hXeXeXeXe

heatXeXe

XeXeeXe

XeXeXe

2*2

*

***

**2

2

hXeXeXe 2*

LAr128~

LXe175~

LNe5.77~

Effect of Ionization Density on Time Dependence

A.Hitachi PRB 27 (1983)5279

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..)

AchievedAchievedAchievedAchievedAchievedAchievedAchievedAchieved

Purification of 22 kg of Xe ongoing Tools Developed_Done for XENON10

Tools Developed_Done for XENON10All major components screened

AchievedVerified Hamamatsu #’s

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

p(t,3He)n

Borated Polyethylene

Lead

LXe

L ~ 20 cm

BC501AUse pulse shape discrimination and ToF to identify n-recoils

Columbia RARAF2.4 MeV neutrons

Aprile et al., Phys. Rev. D 72 (2005)

[Columbia and Yale]

Xe-Recoils Ionization Yield

• 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.

Energy threshold: 10 keVr

[Columbia, Brown and Case]

ELASTIC Neutron Recoils

INELASTIC 129Xe40 keV + NR

INELASTIC 131Xe80 keV + NR

137Cs source

Upper edge -saturation in S2

AmBe n-sourceNeutron

ELASTIC Recoil

5 keVee energy threshold = 10 keV nuclear recoil

Background discrimination capability

Neutron Inelastic 19F110 keV 40 keV

ELASTIC Nuclear Recoil

Teflon (PTFE)

Liquid Xenon

Gas Xenon

P. Majewski

L.Viveiros/R.Gaitskell

Rejection limited by edge gamma event contamination due to field irregularities

nuclearrecoil electron

recoil

improvement expected with XY position sensitive detector

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 mm2 pixel

Fluctuation of PMT signals (# of pe, gain,

analysis error)+

Uncertainties from simulation

(geometry, statistical)

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

Edge events can be well identified

Pos III

Co-57(Pos I)

Co-57(Pos III)

Co-57(Pos II)

Pos II

Pos I

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 (129Xe)+ NR

80 keV Inelastic (131Xe)

110 keV inelastic (19F)+ NR

Neutron Elastic Recoil

40 keV Inelastic (129Xe)+ NR

80 keV Inelastic (131Xe)+ NR

XENON10: Expected Position Sensitivity from Simulation

Assumptions for GEANT4 Simulation

48 PMTs on top, 41 on bottom8 inch diameter, 6 inch drift length

about 15 kg liquid xenon

8 inches

Fitting from measurements by Columbia and XENON Collaborators (En

in keVr), see: Aprile et al., Phys. Rev. D 72 (2005) 072006 Aprile et al., astro-ph/0601552

Top PMT Array Bottom PMT Array, meshes, PTFE

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

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

nn

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

S1 S2

1st step

2nd step

• 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

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

LNGS: March 12, 2006