XENON Collaboration
Experiment Status
“Highlights”
Rick Gaitskell
Brown University, Department of Physics
see information and links at
http://xenon.brown.edu/
Gaitskell
Current XENON Collaboration
Columbia University
+PostDoc
*Grad
Elena Aprile (PI), Karl-Ludwig Giboni, Sharmila Kamat+,
Pawel Majewski+, Kaixuan Ni*, Bhartendu Singh+ and Masaki Yamashita+
Brown University
Richard Gaitskell, Peter Sorensen*, Luiz De Viveiros*
University of Florida
Laura Baudis, David Day*
Lawrence Livermore National Laboratory
Adam Bernstein, Chris Hagmann and Celeste Winant+
Princeton University (move CWRU Jan 2005->)
Tom Shutt, John Kwong*
Rice University
Uwe Oberlack ,Omar Vargas*
Yale University
Daniel McKinsey, Richard Hasty+, Angel Manzur*
Gaitskell Brown University
XENON Collaboration
September 2004 v05 <2>
XENON10 Schematic of Detector and Shield Design
Outer Poly (30cm)
Inner Poly (20cm)
Muon Veto (Plastic Scint.)
not deployed for XENON10 @GS
Pb (22.5cm inc 5 cm ancient liner)
Stainless Steel Cryostat (62kg)
PMTs (Hamamatsu R9288/8520/8778)
Activity for R8778 used as baseline in
simulations
XENON10:
7 inner top PMTs
+16 inner bottom PMTs or CsI Photocath.
+16 outer veto PMTs
Teflon
Xenon Gas
Liquid Xenon – Inner Region
(ø17.5 cm, h 15 cm, 11 kg)
Liquid Xenon – Veto Region
(thickness 5cm, 50 kg)
Copper (2.5cm)
Gaitskell Brown University
(parameters used in Monte Carlos)
XENON Collaboration
September 2004 v05 <3>
Dark Matter Goals
• Dark Matter Goals (labeled on figure)
o
XENON10 - Sensitivity curve corresponds to
~2 dm evts/10 kg/month
• Equivalent CDMSII Goal for mass >100 GeV
(Latest 2004 CDMSII result is x10 above this level)
• With only 30 live-days x 10 kg fiducial - Zero events would reach XENON10 sensitivity goal (90% CL), but we
would like to do physics!
• Important goal of XENON10 prototype underground is to
establish clear performance of systems
o
XENON100 - Sensitivity curve corresponds to
~20 dm evts/100 kg/year
• Background Simulations for XENON10 indicate it could
reach b/g suppression necessary to reach this goal
sensitivity limit (would require some modest upgrabut
with 10 kg target would only give ~2 dm evts/10kg/year no physics.
Gaitskell Brown University
XENON Collaboration
September 2004 v05 <4>
Additional Assumptions
• Monte Carlo Inputs (stated here for the record, won’t discuss in detail)
Assume threshold for full discrimination 16 keVr
o Liquid Xe (3 regions)
o
• LXe Fiducial (after any x-y-z position cuts) majority of inner Xe / LXe Inner (surrounded by Teflon wall - low Kr content)
/ LXe Veto (Xe outer layer, 5 cm simulated)
o
Nuclear/Electron Recoil Quenching Factor Primary Light (QFprimary)
• Zero Field (Conservative) QFp = 20%
• High Field (5 keV/cm) QFp = 50%
— Electron
recoil primary light yield reduced to 38-36%@ 1-5 kV/cm, (vs zero field) due to ionization component no longer
recombining
— Nuclear recoil primary light yield ~90%@5 kV/cm (vs zero field)
o
Background Discrimination
•
•
•
•
o
Electron Recoil assumed 99.5% (1 in 200) above threshold of 8 keVee/16 keVr
Monte Carlo results focus on rates for region 8-16 keVee (16-32 keVr)
External 5 cm LXe veto (Assumed 50 keVee threshold)
Multiple scatter cut within inner region (Dxy = 5cm, Dz = 1cm)
Radioactivity of Components
• Taken from direct measurements U/Th/K/Co (unless otherwise stated)
Gaitskell Brown University
XENON Collaboration
September 2004 v05 <5>
Progress & Some of Remaining Challenges 2002-2004
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PMTs operation in LXe
~1 meter e in LXe
CsI photocathode immersed in LXe
Operating ~few kV/cm electric field
Electron extraction to gas phase
Electron/Alpha recoil discrimination
Efficient & Reliable Cryogenic System
Achieved
Achieved
In progress
Achieved
Achieved
Achieved
Achieved
Technology in place in 10 kg above ground Prototype
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QF measurement with neutron beam
Low Electron/Nuclear recoil discrimination
Kr removal
Background Simulations
Materials Screening
HV system for 15 cm drift ~5 kV/cm
Alternatives to PMT (beyond XENON10)
Gaitskell Brown University
XENON Collaboration
Done; analysis on-going
In progress, move to 10kg
Small prototype studied
Done
on-going (SOLO)
Testing
on-going
September 2004 v05 <6>
XENON Event Discrimination:
Electron or Nuclear Recoil?
Within the xenon target:
• Neutrons, WIMPs => Slow nuclear recoils =>
PMT Array
(not all tubes shown)
strong columnar recombination
=> Primary Scintillation (S1) preserved, but Ionization
Time
(S2) strongly suppressed
• , e-, , (etc) => Fast electron recoils =>
Gas phase
=> Weaker S1, Stronger S2
Proportional
Ionization signal from nuclear recoil too small to be directly
detected => extract charges from liquid to gas and detect ~1 µs width
much larger proportional scintillation signal => dual phase
0–150 µs
depending on
depth
Simultaneously detect (array of UV PMTs) primary (S1) and
proportional (S2) light =>
Primary
Distinctly different S2 / S1 ratio for e / n recoils
~40 ns width
provide basis for event-by-event discrimination.
Challenge: ultra pure liquid and high drift field to preserve
small electron signal (~20 electrons) ; efficient extraction
into gas; efficient detection of small primary light signal
(~ 200 photons) associated with 16 keVr
Light Signal
UV ~175 nm
photons
e-e- ee-
Anode
EAG
e-e- eee-e- ee-
Electron Drift
~2 mm/µs
Liquid phase
Liq. Surface
Grid
EGC
Cathode
EAG > EGC
Interaction (WIMP or Electron)
Gaitskell
Addition of CsI Photocathode at base
CsI is possible option being
evaluated for prototype design
A tertiary signal can be generated
from absorbing primary photons by
CsI photocathode in LXe:
- No transmission loss
- high QE 30%
PMT Array
(not all tubes shown)
Time
CsI Tertiary
Gas phase
Note: 16 keV nuclear recoil:
≈ 200 photons
before applying efficiencies for
geometry and PMT QE.
Also ionization signal
≈ 7-20 electrons
(assumes high field 8 kV/cm)
Anode
EAG
150 µs
(if 30 cm
chamber)
Liq. Surface
Grid
EGC
Primary
~40 ns width
eLight Signal
UV ~175 nm
photons
e-
CsI
Cathode
EAG > EGC
Interaction (WIMP or Electron)
Gaitskell
Available Signal in Liq. Xe (# of photons & electrons for 1 keV event)
SUMMARY OF PARAMETERS FROM EXISTING MEASUREMENTS
Zero Field
High Field
0 V/cm
8 kV/cm
GAMMA EVENT - 1 keV electron equivalent energy
UV Photons
60-75 UV
Electrons+Ions
[60-75 elec]
NUCLEAR RECOIL EVENT UV Photons
Electrons+Ions
1 keV recoil energy
12-18 UV
[12-18 elec]
EFFECTIVE (NR/GAMMA) "QUENCHING FACTOR"
UV Photons
20-25%
Electrons+Ions
[20-25%]
20-30 UV
50-60 elec
11.6 UV
0.4-1.2 elec
30-50%
0.8-2%
• Summary
The ranges shown reflect spread in existing experimental measurements
o Note that the table considers signal from either 1 keV gamma or nuclear recoil event
o 60 excitations / keV is equivalent to ~16 eV / excitation
o Zero field electron-ion #’s in [ ] are inferred, but are signal is not measured (extracted) directly
o
Gaitskell Brown University
XENON Collaboration
September 2004 v05 <9>
XENON R&D: Dual Phase 3D XeTPC Prototype
XENON Set-up at Columbia Nevis Lab
CsI PC in LXe.
• Pulse Tube Refrigerator used to liquefy and maintain LXe at –95.1 ± 0.05 C
• Array of 7 PMTs (Hamamatsu R9288) directly coupled to the Xe active volume
• Fast and Slow digitizers for direct and proportional light waveforms
• Drift Field > 1kV/cm; Extraction Field > 10 kV/cm
'03
• Calibration with gamma (Co-57), alpha (Po-210) and neutron (AmBe)Sept.
sources.
Gaitskell Brown University
XENON Collaboration
September 2004 v05 <10>
TPC and PMTs Details
Gaitskell Brown University
XENON Collaboration
September 2004 v05 <11>
Precise, Stable Cryogenics
- Pulse Tube Cryocooler (Iwatani)
- 100W Cooling Power @ 165 K
- 3.5kW He compressor, water cooled
-Used for pre-cooling (10W) and Xe liquefaction
(45W) @ 5 slpm
- 20W heat loss (insulation not yet optimized)
Temperature Stability
Feb 2-12, 2004
+ Particularly Essential because PMT gain and
Electroluminesence are T/P-dependant.
+ Safety: emergency recooperation of Xe demonstrated
Gaitskell Brown University
XENON Collaboration
September 2004 v05 <12>
XENON100:Cryogenic System and Xe Purification
~ 120 liters of LXe for target and shield. Pulse Tube Refrigerator with ~ 100 W cooling power
(heat load on the XENON100 detector estimated at ~ 50W), used for keeping LXe at – 100 C
within 0.1 degree. Pre-cooling (~1 day) and Xe liquefaction (~2 days) with same PTR.
Hot Getter: Ba/Ti/V Pellets 350 degC - Remove H2O+O2, but not hot enough for more
complex molecules. Ti Spark Purifier
will be evaluated.
September 2004 v05 <13>
Gaitskell Brown University
XENON Collaboration
> 1m Drift Electron Attenuation Length
XENON goal of 30 cm drift and ~few kV/cm E-field necessary for detection of ~ 20 e- signal
(from 16 keV Xe recoil); requires purity < 1 ppb O2 equivalent.
Have built & tested a dedicated Gas Purification System with continuous circulation through
High-temp Getter.
Gaitskell Brown University
XENON Collaboration
September 2004 v05 <14>
Typical Light Waveforms from Dual Phase Chamber
Localized ionization clouds liberated by alphas & 122 keV gammas
Source below TPC --> photoelectric absorption events --> e- drift full LXe gap
Gaitskell Brown University
XENON Collaboration
September 2004 v05 <15>
Dual-Phase Discrimination
Primary/Secondary Discrimination
Gaitskell Brown University
XENON Collaboration
September 2004 v05 <16>
R&D Milestone: Light Detection with UV PMTs in LXe
4.5kg
Xe
Circulation
Gaitskell Brown University
•
Gridded Ionization Chamber (2 cm drift) viewed by
2 Hamamatsu R9288 with custom-developed HV
divider also in LXe.
•
Demonstrated reliability of operation at –100 C and
3 atm. Measured single P.E. level. Gain calibration
with blue LEDs.
•
Demonstrated compatibility of materials with high
purity LXE requirement. Tested and optimized gas
circulation performance and effectiveness. t~ 1ms.
XENON Collaboration
September 2004 v05 <18>
Charge (Q amp) & Light Chamber in 3L chamber
Best D E / E in LXE from light.
Sensitivity Ideal for Quenching
Factor Measurement with < 50 keV
Neutron Recoils
57
Co (122keV)
Best D E / E in LXe from
simultaneous measurement of anticorrelated charge and light signals
137
Cs (662keV)
Light
σ/E = 8.8 %
Light
3.5 p.e./keV
Charge
Charge +Light
Gaitskell Brown University
XENON Collaboration
σ/E = 1.7 %
September 2004 v05 <19>
Hamamatsu PMT Selection
Improvement in b/g’s of PMTs to ~20 mBq has
been impressive (driven by XMASS). PMTs for
XENON10/100 a realistic choice
• Hamamatsu Low Background PMTs
o
The isotopes contribute differently to event rate in (8<E<16keVee) window. For inner PMTs the following
concentrations (mBq/tube) of isotopes give the same event rates (238U/ 232Th/ 40K/ 60Co)
— All
Xe Events:
— Xe Fiducial Anti-Coincident, Single Scatter Events:
Model
R6041
R9288
Photo
(not
same
scales)
Dimension
& QE
ø5 cm x 4 cm
QE 5-8%
ø5 cm x 4 cm
QE 20%
R8520
(2.5
QE >20%
R8778
ø5 cm x 12 cm
QE 26%
Radioactive Background
[mBq/tube]
U Series
Gaitskell Brown University
Th Series
40K
360
90
5040
60Co
10
33.9 mBq – 238U equivalent
(Use of Kovar for most of base)
10
10
120
3
0
5
23.7 mBq – 238U equivalent
(expect further improvement)
13
4
60
XENON Collaboration
Specifically designed for ops in LiqXe
TPC
Evolution of 6041
3
22.8 mBq – 238U equivalent
15
Base Components lower
activity, than these #’s
Comment
680 mBq – 238U equivalent
(Dominated by glass seal at base)
cm)2x3.5cm
(good dyn optics)
10 / 6 / 319 / 23 mBq
10 / 10 / 461 / >80 mBq
3
Square/quad anode
good fill factor (66.2%).
Columbia tested at 150K/4 atm
Designed for XMASS.
Coverage Area: 49.7%
Columbia tested at 150K/4 atm
September 2004 v05 <20>
The simulation is run with a source that simulates the emission lines of the 20 physical PMTs. For this
simulated PMT, we used the Hammamatsu R8778 tube.
2D “Hitogram” – Energy vs. Depth
Gaitskell Brown University
XENON Collaboration
September 2004 v05 <21>
Inner Chamber PMT Gamma Background
• Inner PMTs -- Hamamatsu 8778 (232Th/238U/40K/60Co):
o
Spatial Distribution and Energy Histogram for Events Detected in Inner Chamber
XENON10 Target
XENON10 Target x0.1
XE10/10
Gaitskell Brown University
XENON Collaboration
September 2004 v05 <23>
Stainless Steel Gamma Background
• Gamma Background from Stainless Steel Cryostat below XENON100 target - Liquid
Xenon Veto provides excellent shield against radiation from Cryostat
o
Double-walled Cryostat, each wall 1/8” thick, total 50kg
o
Activity (per kg): 60Co: 23mBq / 238U: 3.5mBq / 232Th: 2.7mBq
Inner Chamber Events (8 < E < 28 keV)
Energy Histogram
Anti-Coincident Inner Events (8 < E < 100keV)
Spatial Distribution
XENON10 Target
XENON10 Target / 10
XE10/10
XE10/10
Gaitskell Brown University
XENON Collaboration
September 2004 v05 <24>
XENON10 – Gamma/Electron Background Event Rates
• Gamma Background Event Rates (8 < E < 16keVee) for XENON10 Module
XENON10 Goal is 160 mdru gammas before electron recoil rejection
o XENON100 Goal (16 mdru) can also be achieved using anti-coin. LXe Veto and multiple scatters cut
o All rates quoted before assumed 99.5% electron recoil rejection vs nuclear recoil signal
o
Source
Inner Event Rate (only z cut)
(8 < E <16 keVee) [ mdru ]
Inner Event Rate with extra cuts:
Anti-Coincid. with LXe outer
+ single scatter cut
(8 < E <16 keVee) [ mdru ]
7 Inner PMTs
38
3.5
16 Outer PMTs
8.3
<0.1
HV Shaping Ring Resistors
6.8
1.6
Stainless Steel Cryostat
33
5.7
6
6
Lead
-
-
(PMT Neutrons)
( 10-5 )
( 10-6 )
Total
92 mdru
16.8 mdru
85Kr
(@ 0.1 ppb)
Event Rate Tables for External Neutrons are dealt with in Appendix
Gaitskell Brown University
XENON Collaboration
mdru = 10-3 evts/keVee/kg/day
September 2004 v05 <25>
R&D Milestone: Primary Light QF Measurement
Existing published data are inconsistent & do not extend to the
low-energy (~10-30 keV) region, of interest to next-generation DM
searches:
LXe Recoil (keV)
Measured QF
Authors
40 - 70
0.22 ± 0.01
Akimov, et. al.
2002
45 - 110
~ 0.2
Arneodo, et. al.
2000
35 - 70
0.45 ± 0.10
Bernabei, et. al.
2001
CU RARAF 2.2 MeV neutrons
p(t,3He)n
Borated
Polyethylene
Lead
LXe
L ~ 20 cm

BC501A scintillator tags recoil events:
Gaitskell Brown University
XENON Collaboration
BC501A
Using pulse shape
discrimination and time
of flight to BC501A to
identify neutron recoils
September 2004 v05 <26>
Preliminary Results: Low Energy Quenching Factor
(Zero Applied Field)
56.5 keV NR
15.5 keV NR
Aprile et al., analysis on-going
(current plots not to be considered definitive)
- Electron equivalent Energy scale calibrated with 57Co spectrum & compared with MC
- Multiple scattering makes low-E data more difficult to interpret
Gaitskell Brown University
XENON Collaboration
September 2004 v05 <29>
Field Dependence of Primary Nuclear Recoil Scintillation
~90% light yield at high field, similar
to alpha recoil…
Aprile et al., in preparation
Gaitskell Brown University
XENON Collaboration
September 2004 v05 <31>
Burle Industries MicroChannel Plate (MCP 85006)
MCP similar gain to PMT / better form factor / BG similar
Fast 1 ns electronic pulse width
30% QE of Photocathode best performance of ANY photo
sensor we have tested.
Pulse Area Spectrum from 207Bi
~80 keV x-rays
1000
160
~100 phe pulse
~750 phe / 80 keV
100
80
~30 keV x-rays!
mV
cts
0
10
1000
Gaitskell Brown University
3000
5000
phe
XENON Collaboration
5x5 cm enclosure - MCP removed,
leaving 4 separate anodes visible.
0
50
100
ns
September 2004 v05 <32>
Summary: XENON R&D Goals and Status
• XENON Above Ground R&D Program: Goals achieved
> 1 meter electron drift attenuation length in LXe
o Reliable Operation of UV PMTs in LXe
o LXe Cryogenics System with Pulse Tube Refrigerator
o Dual Phase Operation with 7PMTs 100 % Electron Extraction
o Novel HV Distribution to PMTs Array in LXe
o Detector Simulations of E-Fields / Light Collection/ 3D TPC
o Low Radioactivity PMTs (with ~10-100 mBq/2” tube)
o MC Background Simulations
o Xe Nuclear Recoils (10 –100 keV) Scintillation Efficiency and its
Field Dependence ‡ (paper in preparation)
o
• R&D Goals Underway:
Xe Nuclear Recoils (10 –100 keV) Ionization Efficiency and its
Field Dependence
o Demonstrate Electron / Nuclear Recoil Discrimination down to
16 keVr with PMTs coverage on bottom (~2.3-2.6 p.e./keV)
o Combine Xe gas purification with Kr separation system ( < 0.1
ppb )
o Finalize Materials Screening and selection for XENON10
o
• Construction of Underground Infrastructure/Shield Jul 05 –>
• Operate 10 kg system underground Jan 06 –>
Gaitskell Brown University
XENON Collaboration
September 2004 v05 <34>