The%20XENON%20Project

1
The XENON Project

• A 1 tonne Liquid Xenon experiment for a sensitive
  Dark Matter Search
• Elena Aprile
• Physics Department, Columbia University

2
The XENON Project Overview

• Outline
• Science Motivation and Goals Overview
• Dark Matter Direct Searches Worldwide
• LXe Properties relevant to WIMP Detection
• XENON Instrument Design Overview
• Comparison with other LXe Projects
• XENON Team Presentations
• XENON Organization and Management

3
The XENON Collaboration

• Columbia University E. Aprile (Principal
  Investigator)
• T. Baltz, A. Curioni, K-L. Giboni, C. Hailey, L.
  Hui, M. Kobayashi and K. Ni
• Brown University R. Gaitskell
• Princeton University T.Shutt
• Rice University U. Oberlack
• LLNL W. Craig

4
Why should NSF support XENON

• Because a WIMP experiment with discovery
  potential will have enormous scientific impact
  in particle physics and astrophysics. Need to
  validate discovery with different targets and
  technology.
• Because the timing is right and the proposed
  XENON concept is based on a relatively simple
  technology with unique suitability for the
  1-tonne scale required by the science.
• Because the proposing team combines extensive
  experience with large scale LXe detectors with
  complementary experience in other key areas
  required for a successful realization of the
  XENON dark matter project!

5
The Case for Non-Baryonic Dark Matter

• Standard BBN calculations 4He and D primordial
  abundance
• Obh2 0.020 0.001
• (APJ, 552, L1, 2001)
• Measurements of the matter density
• Om 0.2 0.4
• hH0/100 kms -1Mpc-1 (h 0.6 0.8)
• Cluster velocity dispersion (Mass to Light ratio)
• Galactic rotation curves
• Cluster baryon fraction from X-ray gas
• CMB anisotropies give Omh2 0.15 0.05 (APJ,
  549, 669, 2001)
• and also confirms Obh2 0.02
• Om gtgt Ob

6
Non-baryonic Dark Matter Candidates

• Neutrinos hard to make up a significant fraction
  of mass density with neutrinos, unless much more
  massive than observed
• ?m lt 0.1 eV ( PRL 81(1998)1562)
• Axions strong CP, m 10-5eV, search is in
  progress using microwave cavities ( PRL
  80(1998)2043)
• Massive Compact Halo Objects (MACHO) with 10-7 -
  10 Mo cannot account for a large fraction of the
  DM in the Milky Way halo
• (ApJ 550(2001)L169)
• Weakly Interacting Massive Particles (WIMPS)
• Stable (or long lived) particles left over from
  the BB, decoupling when non-relativistic their
  relic density OXh2 1/lt?X vgt
• (?X ?weak) ? OXh2 1

7
Supersymmetry

• Stabilizes MPL and MZ hierarchy
• Unification of coupling constants
• Lightest Super Particle is stable
• Neutralino

SUSY offers the favorite WIMP candidate
Superposition of photino, zino and higgsinos

• SUSY particles were not invented to solve the
  dark matter problem.
• Particles with several 100 GeV/c2 actively being
  pursued at accelerators.
• Direct WIMP searches can probe mass values
  impossible to reach at colliders.
• Typical WIMP nucleon cross sections in the range
  10-5 and 10-11 pb

8
Muon g-2 Measurement

• BNL results on muon anomalous magnetic moment
  disagree with Standard Model at 1.6 ? level (PRL
  86(2001)2227)
• If discrepancy is due to SUSY, a large
  neutralino-nucleon cross section (10-9 pb) and a
  low mass (lt500 GeV) are favored
• World eagerly awaiting for new results from last
  run!

9
WIMP Direct Detection

• Elastic scattering off nuclei in
• laboratory target
• ? measure nuclear recoil energy
• Spin-independent interactions are coherent (? A2)
  at low energy ? dominate for most models. Target
  with odd isotopes needed for spin-dependent
  interactions
• Energy spectrum and rate depend on local dark
  matter density ?0
• measured galactic rotation curve flat out to
  50 kpc with vcir?220 km/s ? spherical halo with
  ?0 ? 0.3-0.5 GeV/cm3 and M-B velocity
  distribution with v ?220 km/s

10
Experimental Challenges

• Recoil energy is small ? few keV ? detectors with
  low threshold
• Event rates are low ltlt radioactive background ?
• detectors with low radioactivity, deep
  underground and with active background rejection

With E0 1/2MX(?0c)2 r 4 MX MA /(MX MA )2 R0
?T?0c?0 c1?0.78 and c2?0.58 Fform factor (see
Phys.Rept.267(1996)195
11
Background Rejection Methods

• Reject events more likely to be due to g, e, a
  radioactivities
• ? multiple-scatters (WIMPs interact too
  weakly) ?HDMS
• ? single-scatters localized near detector
  walls (WIMPs interact anywhere) ?CDMS ZIP
  detectors
• ? electron recoils (WIMPs more likely
  interact with nucleus)
• ?CDMS, EDELWEISS (CRESST, ZEPLINs, DRIFT)
• A 3D LXeTPC like XENON will combine all these
  rejection capabilities
• Use motion of Earth/Sun through WIMP halo
• ? direction of recoil ?DRIFT
• ? annual modulation ? DAMA, NAIAD

12
Expected rates for various targets

For a heavy target nucleus such as Xe, a very low
recoil energy threshold is crucial. The expected
rate, integrated above threshold of 16 keV is 1
events/ kg/day
13
WIMP Direct Searches with Recoil Discrimination
14
Current and Projected Limits of
Spin-Independent WIMP Searches

• Projection for CDMS Soudan (7kg GeSi) and
  competing experiments in Europe, including LXe
  projects of the UKDM program is 1 event / kg /
  yr
• It will take a target mass at 1 tonne scale and
  similar background discrimination power to reach
  a sensitivity of 1 event / 100kg / yr or s
  10-46 cm2
• LXe attractive target for scale-up.
• Projection for XENON based on Homestake,
  99.5 recoil discrimination, 16 keV true recoil
  energy threshold and an overall 3.9x 10-5 cts
  /kg /d /keV background rate.

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Why is Liquid Xenon Attractive for Dark Matter

• High mass Xe nucleus good for scalar interaction
  of WIMPs
• High atomic number (Z54) and density (r3g/cc)
  good for compact and flexible detector geometry.
  Easy cryogenics at 100C
• High ionization (W15.6eV) yield and small Fano
  factor for good DE/E
• High electron drift velocity (v2 mm/ms) and low
  diffusion for excellent spatial resolution.
  Calorimetry and 3D event localization powerful
  for background rejection based on fiducial volume
  cuts and event multiplicity
• High scintillation (W13 eV) yield with fast
  response and strong dependence on ionizing
  particle for event trigger and background
  discrimination with PSD
• Distinct charge/light ratio for electron/nuclear
  energy deposits for high background
  discrimination
• Available in large quantity and easy to purify
  with a variety of methods. Demonstrated electron
  lifetime before trapping of order 1 millisecond
  for long drift. No long-lived radioactive
  isotopes. 85Kr contamination reducible to ppb
  level

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and for Solar n and 0nbb Decay
17
Ionization and Scintillation in Liquid Xenon
I/S (electron) gtgt I/S (non relativistic particle)
Alpha scintillation
Electron charge
L/L0 or Q/Q0 ()
electron scintillation
Alpha charge
Electric Field (kV/cm)
18
Electron vs Nuclear Recoil Discrimination (Direc
t Proportional Scintillation )
Measure both direct scintillation(S1) and
charge (proportional scintillation) (S2)
Dual Phase Detection Principle Common to All LXe
DM Projects

• Nuclear recoil from
• WIMP
• Neutron
• Electron recoil from
• gamma
• Electron
• Alpha

Gas
1µs
anode
grid
Drift Time
e-
Proportional scintillation depends on type of
recoil and applied electric field. electron
recoil ? S2 gtgt S1 nuclear recoil ? S2 lt S1 but
detectable if E large
E
Liquid
40ns
cathode
19
The XENON Experiment Design Overview

• The XENON design is modular.
• An array of 10 independent 3D position sensitive
  LXeTPC modules, each with a 100 kg active Xe
  mass, is used to make the 1-tonne scale
  experiment.
• The fiducial LXe volume of each module is
  self-shielded by additional LXe. The thickness
  of the active shield will be optimized for
  effective charged and neutral background
  rejection.
• One common vessel of 60 cm diameter and 60 cm
  height is used to house the TPC teflon and copper
  rings structure filled with the 100 kg Xe target
  and the shield LXe (50 kg ).

20
The XENON TPC Principle of Operation

• 30 cm drift gap to maximize active target ? long
  electron lifetime in LXe demonstrated
• 5 kV/cm drift field to detect small charge from
  nuclear recoils ? internal HV multiplier
  (Cockroft Walton type)
• Electrons extraction into gas phase to detect
  charge via proportional scintillation (1000 UV
  g/e/cm)? demonstrated
• Internal CsI photocathode with QE31 (Aprile et
  al. NIMA 338,1994) to enhance direct light
  signal and thus lower threshold ? demonstrated
• PMTs readout inside the TPC for direct and
  secondary light ? need PMTs with low activity
  from U/Th/K

21
The XENON TPC Signals

• Three distinct signals associated with typical
  event. Amplification of primary scintillation
  light with CsI photocathode important for low
  threshold and for triggering.
• Event depth of interaction (Z) from timing and
  XY-location from center of gravity of secondary
  light signals on PMTs array.
• Effective background rejection direct consequence
  of 3D event localization (TPC)

22
Detection of LXe Light with a CsI Photocathode

• Stable performance of reflective CsI
  photocathodes with high QE of 31 in LXe has been
  demonstrated by the Columbia measurements
• CsI photocathodes can be made
• in any size/shape with uniform response, and
  are inexpensive.
• LXe negative electron affinity Vo(LXe) - 0.67 eV
  and the applied electric field explain the
  favorable electron extraction at the CsI-liquid
  interface.

Aprile et al. NIMA 338(1994) Aprile et al. NIMA
343(1994)
23

Light Collection Efficiency MonteCarlo

• Assumptions
• Wph 13 eV
• lph 1.7 m
• Quenching Factor 25
• Q.E. of PMTs 26
• Q.E. of CsI 31
• R.E of Teflon Wall 90
• Mass of Liquid Xe 100 kg
• 37 PMTs (2 inch) array

24
Simulation Results

• A 16 keV (true) nuclear recoil gives 24
  photoelectrons. The CsI readout contributes the
  largest fraction of them.
• Multiplication in the gas phase gives a strong
  secondary scintillation pulse for triggering on
  2-3 PMTs.
• Coincidence of direct PMTs sum signal and
  amplified light signal from CsI
• Main Trigger is the last signal in time sequence?
  post-triggered digitizer read out Trigger
  threshold can be set very low because of low
  event rate and small number of signals to
  digitize. PMTs at low temperature? low noise.
• Even w/o CsI (replaced by reflector) we still
  expect 6 pe . Several possible ways to improve
  light collection.

25
Summary of Previous Nuclear Recoil Measurements
(Quenching Factor)
? previous measurements have wide scatter ? no
measurements at all at low energies ? results
consistent with Lindhard theory
26
We have experience measuring neutron-nuclear
recoil efficiency
typical setup for measurement of nuclear recoil
scintillation efficiency at University of
Sheffield
measured low energy nuclear recoil efficiency of
liquid scintillator Hong, Hailey et. al., J.
AstroParticle Physics 2001
2.9 MeV neutron beam
27
Why Do Nuclear Recoil Scintillation Efficiency
Measurements?

• Confirm that measured efficiency at higher
  energies extends down to lowest energies of
  interest to a WIMP search
• Confirm result in our particular experimental
  configuration.
• Results can vary with Xe purity, light
  collection efficiency etc.
• Measure true nuclear recoil scintillation pulse
  shapes

28
Charge readout with GEMs a promising
alternative

• High gain in pure Xe with 3GEMs demonstrated
• Coating of GEMs with CsI
• 2D readout for mm resolution

See Bondar et al.,Vienna01
29
XENON Technical Heritage LXeGRIT

• A 30 kg Liquid Xenon Time Projection Chamber
  developed with NASA support. 3D imaging detector
  with good spectroscopy is the basis of the
  balloon-borne LXeGRIT, a novel Compton Telescope
  for MeV Gamma- Ray Astrophysics.
• The LXeTPC operation and response to gamma-rays
  successfully tested in the lab and in the harsh
  conditions of a near space environment.
• Road to LXeGRIT extensive RD to study LXe
  ionization and scintillation properties,
  purification techniques to achieve long electron
  drift for large volume application, energy
  resolution and 3D imaging resolution studies,
  electron mobility etc.

30
A Liquid Xenon Time Projection Chamber for
Gamma-Ray Astrophysics
31
The Columbia 10 liter LXeTPC

• 30 kg active Xe mass
• 20 x 20 cm2 active area
• 8 cm drift with 4 kV/cm
• Charge and Light readout
• 128 wires/anodes digitizers
• 4UV PMTs

32
High Purity Xenon for Long Electron Drift and
Energy Resolution
And the power of Compton Imaging
33
Compton Imaging of MeV g-ray Sources
34
3D capability for event discrimination Flight
Data
35
From the Lab to the Sky The Balloon-Borne Liquid
Xenon Gamma-Ray Imaging Telescope (LXeGRIT)
LXeGRIT inflight energy spectra
Compton Imaging Events
Atm/Cosmic Diffuse MC simulation and Data
36
Background Considerations for XENON

• ? and ? induced background
• 85Kr (?1/210.7y) 85Kr/Kr ? 2 x 10-11 in air
  giving 1Bq/m3
• Standard Xe gas contains 10ppm of Kr??10 Hz
  from 85Kr decays in 1 liter of LXe.
• Allowing lt1 85Kr decay/day i n XENON energy
  band ? lt1 ppb level of Kr in Xe
• 136Xe 2??? decay (?1/28 x 1021y) with Q 2.48
  MeV expected rate in
• XENON is 1 x 10-6 cts/kg/d/keV before any
  rejection
• Neutron induced background
• Muon induced neutrons spallation of 136Xe and
  134Xe ? take 10 mb and Homestake 4.4 kmwe?
  estimate 6 x 10-5 cts/kg/d before any rejection
• ? reduce by muon veto with 99 efficiency
• (?,n) neutrons from rock ?1000/n/m2/d from (?,n)
  reactions from U/Th of rock
• ? appropriate shield reduces this background to
  ?1 x 10-6 cts/kg/d/keV
• Neutrons from U/Th of detector materials within
  shield, neutrons from U/Th of
• detector components and vessel give?? 5 x 10-5
  cts/kg/d/keV
• ? lower it by x10 with materials selection

37
Background Considerations for XENON

• ? -rays from U/Th/K contamination in PMTs and
  detector components dominate the background rate.
  For the PMTs contribution we have assumed a low
  activity version of the Hamamatsu R6041 ( ? 100
  cts/d ) consistent with recent measurements in
  Japan with a Hamamatsu R7281Q developed for the
  XMASS group (Moriyama et al., Xenon01 Workshop).

Numbers are based on Homestake location and
reflect 99.5 background rejection but no
reduction due to 3D imaging and active LXe
shield.
38
How is XENON different from other Liquid Xe
Projects?
39
UCLA ZEPLIN II
40
ZEPLIN II
41
ZEPLIN II ? ZEPLIN IV
30 kg ? 1000 kg
The latest design as at DM2002
42
UKDM ZEPLIN III
43
ZEPLIN III
44
The LXe Program at Boulby
45
The LXe Program at Kamioka
XMASS
present
Cold finger
with new PMTs no rejec.
gas filling line
Wire set (Grid1,Anode Grid2)
with 99 rejection
PTFE Teflon (Reflector)
Gas Xe
MgF2 Window with Ni mesh (cathode)
Liq. Xe(1kg) 9.5 cm Drift
OFHC vessel (5cm)
PMT
46
Signals from 1kg XMASS Prototype
42000photon/MeV Decay time 45nsec
direct
direct
direct
proportional
drift time
drift time
proportional
47
XMASS Recoil /? ray Separation
gt99 ? ray rejection
22 keV gamma ray
Proportional scintillation(S2)
Recoil Xenon (neutron source)
Direct scintillation(S1)
(Ref. JPS vol.53,No 3,1998, S.Suzuki)
48
XMASS low activity PMT development
57 Co (122keV)
s/E 15 2.4 p.e./keV at 250V/cm
counts
with R7281MgF2 (Q.E.30) (HAMAMATSU(prototype)
A low activity version of this tube shows 4.5
10-3 Bq!
p.e.
137Cs 662keV
Towards a 20 kg Detector
counts
p.e.
49
Answer to Question

• LXe long recognized as promising WIMP target for
  a large scale experiment with relatively simple
  technology. So far however development effort has
  been subcritical.
• Low energy threshold and background rejection
  capability yet to be fully demonstrated.
• Recent move to an underground lab - 1 kg XMASS
  detector in Kamioka- an important milestone.
  Scale up to a 20 kg detector of same design (7
  PMTs vs 1) started.
• UCLA ZEPLIN II is similar in size and design to
  XMASS drift in LXe over 10 cm with low
  electric. Secondary light pulse from low energy
  nuclear recoils hard to detect. Scale up to 1
  tonne with a monolithic detector (ZEPLIN IV) too
  risky and unpractical.
• UKDM ZEPLIN III better discrimination power and
  lower threshold due to high electric field.
  Design does not present an easy scale up from 6
  kg to sizable modules of order 100 kg.
• XENON combines the best of the techniques with a
  design which can be easily scaled. Strength of
  experience with a 30 kg LXeTPC for gamma ray
  astrophysics critical mass at Columbia with
  collaborators key experiences in DM searches.

50
XENON Phase 1 Study 10 kg Chamber

• Demonstrate electron drift over 30 cm
  (Columbia)
• Measure nuclear recoil efficiency in LXe
  (Columbia)
• Demonstrate HV multiplier design (Columbia)
• Measure gain in Xe with multi GEMs (Rice and
  Princeton)
• Test alternative to PMTs, i.e. LAAPDs (Brown)
• Selection and test of detector materials (LLNL)
• Monte Carlo simulations for detector design and
  background studies (Columbia /Princeton/Brown)
• Study Kr removal techniques (Princeton)
• Characterize 10 kg detector response and with g
  and neutron sources (Entire Collaboration)

51
What next? XENON and NUSL

• The result of the 2yr Phase 1 will be a working
  10 kg prototype with demonstrated low ER
  threshold and recoil discrimination capability.
  Its move to a deep underground location will
  initiate science return.
• Phase 2 is for construction and operation of a
  100 kg module as 1st step towards 1 tonne. We
  plan to seek DOE and NSF support and more
  collaborators
• By this time the situation of a NUSL will be
  clear. If NUSL is delayed, several alternative
  locations possible ( Boulby, GS, WIPP, etc.)but
  deeper the better..

52
Summary

• Liquid Xenon is an excellent detector material
  well suited for the large target mass required
  for a sensitive Dark Matter experiment.
• The XENON experiment is proposed as an array of
  ten independent, self shielded, 3D position
  sensitive LXeTPCs each with 100 kg active mass.
• The detector design, largely based on established
  technology and gt10 yrs experience with LXe
  detectors development at Columbia, maximizes the
  fiducial volume and the signal information useful
  to distinguish the rare WIMP events from the
  large background.
• With a total mass of 1-tonne, a nuclear recoil
  discrimination gt 99.5 and
• a threshold of 16 keV, XENON expected
  sensitivity of ? 0.0001 events/kg/day in 3 yrs
  operation, will cover most SUSY predictions.

53
XENON Organization
Subsystem responsibility is allocated amongst the
team of experienced co-investigators.
54
XENON Management Approach

• Phase I of the XENON project spans a 2 year
  period from the funding start date. This
  instrument development effort has the focused
  goal of a clear demonstration of the capabilities
  of a 10 kg LXe detector for a sensitive Dark
  Matter search.
• The 10 kg prototype defines the roadmap to the
  Phase II development of a 100 kg detector as one
  unit of a 1 tonne scale XENON experiment.
• In complexity, the XENON Phase I development does
  not exceed the NASA funded LXeGRIT experiment and
  we adopt the successful practices developed
  during this project.
• We have the required critical mass with
  extensive expertise in LXe detector technology
  and other areas relevant to a Dark Matter
  experiment. This, plus sensible management
  practices will insure meeting the milestones
  promised by the end of the 2nd year of Phase I.

55
Management Activities

• To coordinate the efforts and insure the
  appropriate level of communication and exchange
  of information between the Columbia team and team
  members at Brown, Princeton, Rice, and LLNL the
  PI will
• organize bi-weekly videoconference meetings
• obtain monthly progress reports on all sub
  systems
• organize semi annual project reviews with
  participation of collaborators and external
  advisors
• prepare yearly progress reports for NSF
• encourage student/minority involvement in the
  research
• take full responsibility for the key deliverables
  to NSF by end of Phase I

56
Development Schedule

• Year 1 activities concentrate on
• Monte Carlo simulations to guide the design
• Gas system construction and testing
• Neutron recoil efficiency measurements
• Baseline detector development
• Alternative detector development
• Materials selection and testing

57
Development Schedule (2)

• Year 2 activities concentrate on
• Build of the 10kg prototype
• Demonstration of Krypton reduction
• Design of the 100kg instrument
• End of Phase I results in near final design of
  100kg module and demonstration of all key
  technologies in the 10 kg prototype.

58
Team Members Expertise
59
Budget Details
Year 1 request 823k Year 2 request 873k
Budget breakout (of 2 year total) is consistent
with our fast track development of a working
prototype
60
Team Members Presentations
61
Materials Selection and Testing
Bill Craig (LLNL)

• Candidate material selection will begin with
  study of existing databases assembled for other
  projects.
• LLNL personnel (Craig, Ziock) are associated with
  ongoing projects requiring low background and
  will use this existing infrastructure to do
  testing of candidate materials.
• Close coupling between this effort and the XENON
  10/100 kg design team to ensure optimal material
  choices are incorporated as quickly as possible.