t. shutt- the xenon dark matter search
TRANSCRIPT
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The XENON
dark matter search
T. Shutt
CWRU
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The XENON collboration
Columbia UniversityElena Aprile (PI), Edward Baltz ,Karl-Ludwig Giboni, Sharmila Kamat,
Pawel Majewski ,Kaixuan Ni, Bhartendu Singh, and Masaki YamashitaRice University
Uwe Oberlack ,Omar VargasCase Western Reserve University
Alex Bolozdynya, Eric Dahl, Jennifer Kalb, John Kwong, Tom Shutt,Matt Whilden
Brown University
Richard Gaitskell, Peter Sorensen, Luiz DeViveirosLawrence Livermore National Laboratory
Adam Bernstein, Chris Hagmann and Celeste Winant
University of FloridaL. Baudis, J. Orboek, A. ManalaysayYale University
D. McKinsey, R. Hasty, A. Mazur
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CDMSII
Edelweiss
Current limits
~ 0.1 cnts/
kg/day
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How big?
Motivation for very large detector clear
"Generic" test of MSSM possible with 1-10 tons
Less restrictive framework can allow lower rates
If signal seen, need larger mass to probe modulation.
Current limits: 0.2 event/kg/day
Ellis, Olive, Santoso,Spanos, hep-ph/ 030875
Calculations in minimal supersymmetry framework (MSSM).
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Promise of liquid Xenon. Good WIMP target.
Readily purified
Self-shielding - high density, high Z.
Can separate spin, no spin isotopes129Xe, 130Xe, 131Xe, 132Xe, 134Xe, 136Xe
Rich detection media
Scintillation
Ionization
Scalable to large mass
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Basic processes in liquid Xenon Complicated atomic processes
Scintillation - 175 nm Singlet ( 3 ns), triplet ( 27 ns)
Ionization Recombination (15 ns)
Energy per quanta (electron recoils):
charge: 20 eV
Photon: 20 eV
Difference between e and n recoils
Nuclear recoils, electronic excitations suppressed by 5.
Nuclear recoils suffer recombination
dE
dxv
2
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LXe
PMTs
A. Bolozdynya, NIMA 422 p314 (1999).
WIMP
Dual Phase, LXe TPC
5s/cm
~1 s
---
-
Ed
Es
Time
Time
~40 ns
Very good event location. Good discrimination despite
small number of e-,
Need single charge, photon
sensitivity
Use charge amplification insteadof increasing E/kT.
Competitors: ZEPPLIN II, III
ITEP
XMASS_DM
Ar detectors (Icarus, FLARE)
Charge drift easier.
39Ar background.
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Discrimination of nuclear recoils Electron recoils - background. Gammas, X-rays, betas.
Nuclear recoils - signal: High density track. Charge recombination. Possible changes inscintillation time profile.
Suppression (Lindhard) of both charge and scintillation.
light
Background:
electron recoils
Signal: nuclear recoils
charge
light
Recombination fornuclear recoils
discrimination
Ionization
Scin
tillation
Effect of recombination
(122 keV gammas)Recombinat
ion
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Detectors
2004 - 1 kg LXe
Currently - 3 kg LXe
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Neutron beam calibration of scintillation
Liquid
scintillator
neutron
beam
Liquid Xe
Er= E
n
4mM
m + M
1
2(1+ cos)
Columbia/Yale
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Measured by two groups,detectors. Case
Columbia/Brown
Detectors: 4 cm , 1 & 2cm deep.
Full measurement of nuclear recoils
Charge calibrated directly with 122keV gammas and alphas.
Energy relies on previous n-beamcalibrations.
Note: Columbia geometry has x 5light collection over Case.
PMT in liquid instead of gas.
40keV gamma
(inelastic n-Xe)
206Pb-recoils
Xe recoils from
neutrons
Case
Columbia/Brown
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Preliminary look at discrimination
gammasn-recoils
Neutrons Gamma Background
Limitations: Light collection statistics
With current data, rejection robust ~ 20keV.
Poor charge collection
At edges (only?) Rejection > 104 for alphas in center of
detector.
Currently 98 % at high energies.
Basic processes compatible with very highdiscrimination for E > ~20 keV.
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Ionization yield
Larger than expected based on alphas. Easy to measure!
Not as distinct from gammas as expected.
Physics: dq/dx(E,E) (from dE/dx) + recombination
Surprising field independence
Increase at low energy agrees with dE/dx.
Versus energy Versus electric field
Electr
ons/keVnre
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Quenching Factors vs Drift Field
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
0 1000 2000 3000 4000 5000
Drift Field (V/cm)
Quenchingfactors,normalizedto
full(no)recombinatio
nforlight(charge))
Alpha Charge (Po210)
Gamma Charge (Co57)
Alpha Light (Po210)
Gamma Light (Co57)
LXe processes
New measurement of 122 keV gammas (57Co).
Agreement between single phase and dual phase data.
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Single electrons and photons
Threshold and stability quite important. Electric fields present challenge: 5 kV/cm -
liquid; 12 kV/cm gas.
With single-PMT system, havedemonstrated stable triggering over
2months.
Single photo-
electron threshold
S2: ~ 1.5 electrons
S1: ~ 5 keVnr
Light: < 1 p.e. Issue is light collection.
Charge threshold ~ 1 electron.
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Scintillation peak ~175 nm (VUV).
Total internal reflection n ~ 1.6, 40% transmission (2).
Collection at bottom ~ 5 times better than collection above.
Light collection
Current technology: PMTs in liquid and gas
Hamamatsu 5820, 1 square, 17 % effective QE.
~ 1 p.e./keV for nuclear recoils.
Alternative: CsI photocathode.
PMTs top and bottom, PTFE walls, 4 grids
Top PMT Bottom PMT
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Capacitance level sensor Liquid level critical
With 2, determines field that gives
charge signal.
Sensors: parallel plates capacitors
~ 1-2 pF empty-full
Cx
Zf
Vi ViV
o
=
Z
Zx
Virtual ground readout
f F sensitivity
Independent of stray capacitance.
4 mm
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MC: gamma Background from PMTs
Inner PMTs - Hamamatsu 8778(232Th/238U/40K/60Co):
XENON10 Target
XENON100 Target
PMTs
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Hamamatsu PMTs
34 60
53 0
13
15
310 12010
1090504
0360
Th
Series60Co
U
Series40K
Designed for XMASS.
Coverage Area: 49.7%
Columbia tested at 150K/4
atm
80 mBq(expect further improvement)
5 cm x 12
cm
QE 26%R8778
Square/quad anode-good
fill factor (66.2%).Columbia tested at
150K/4 atm23 mBq
(2.5
cm)2x3.5cm
QE >20%R8520
Evolution of 6041143 mBq
(Use of Kovar for most of base)
5 cm x 4
cm
QE 20%R9288
Specifically designed for
ops in LiqXe TPC
5500 mBq(Dominated by glass seal at base)
5 cm x 4
cm
QE 5-8%
R6041
Comment
Radioactive Background
[mBq/tube]Dimension& QE
PhotoModel
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Gamma/Electron Background MC
(removed by Gas sep./getter)Tritium
9Polyethylene Shield
< 5External/Pb shield Gammas
< 1Teflon Walls
~< 40 mdruTotal
< 5210Pb Brem (Pb shield 30
Bq/kg)
< 685Kr (< 0.1 ppb)
12Stainless Steel Cryostat
1.6HV Shaping Ring Resistors
0.6416 Outer PMTs
9 (5 *)7 Inner PMTs
Rate [ mdruee ]Source
Goal for XENON10, 8 < E < 16keVee: 0.140 cnts/kg/keV/day
before 99.5 % rejection. Assumes using 5 cm outer LXe active veto and inner multiple scatters cut
mdruee = 10-3 evts/keVee/kg/day* if a 1 cm depth cut is made at top of inner LXe
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XENON10 Neutron Background MC
6 *Muon-Induced Neutrons from Poly
Shield
0.01PMT/Stainless Internal (,n) Neutrons
15(,n)/Fission Neutrons from Cavern
10 *Muon-Induced Neutrons from Pb Shield
3 **High Energy Muon-Induced Neutrons
from Rock
34 drurTotal
Inner Event Rate (no cuts)
(@ 2 keVr) [ drur ]Source
Neutron Background Event Rates for XENON10 Module
XENON10 Goal is 1.3 evts/10kg/month =>360 drur (100GeVWIMP)
Assumes LNGS 24 /m2/day (No muon veto required)
drur = 10-6 evts/keVr/kg/day* factor 2 uncertainty
** factor 4 uncertainty
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Kr removal 85Kr (, 687 keV endpoint).
Best commercial Xe: 5 ppbKr/Xe (XMASS)
Goals: XENON10 (100,1000)
< ppb, (100, 10 ppt)
Possible separation methods:
Distillation - (XMASS)
Chromatography.
Kr
Xe
KrXe
charcoal column
Projected performance, 1 Kg
charcoal column:
1.8 Kg Xe/day
Purification 103
Use 14 stp m3 He/ Kg Xe
processed.
High purity system being
commissioned.
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Xe purity - chemical Xe is not so noble.
high polarizability (same as alkanes)
e- attachment during drift
SF6
O2
N2O
Mitigation:
Detector cleanliness, bakeout. Commercial high temp., Zr-based getters
Recirculation in gas phase
Demonstrated: > 1 m drift length.
~ 2 month stability.
1 cm
~ 40 cm
TPC measurement
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XENON10 program Basic R&D demonstrated:
Discrimination of nuclear recoils
at low energy. 1 kg, 7 PMT detector.
> 1 m charge drift.
Stable cryogenics.
3 kg, 21 PMT detector now underoperation.
This fall -> 10 kg detector.PMTs top + bottom.
10 kg detector in Gran Sasso in2006
Field shaping
21 PMT array
(top and bottom)
diving
bell
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Gran Sasso Installation
First installation - modest size. Power: 20 kW, (15 kW UPS)
LN2 (440 liters/week)
100 kg installation will not be
much larger.
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Projected sensitivity
CDMSIIgoa
l
XENON10
XENON100
Edelweiss
XENON1T
CDMSII
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For a large-scale experiment
Purification in liquid phase - sparkpurifier
CsI photocathode
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CsI photocathode
Gate
Transmission
Anode
CsIphotocathode
Edrift
E1
E1E
0
E1
Gated
Edrift
PMT PMT
Positive feedback: gating required.
CsI photocathode good match to thisapplication
VUV sensitive, "robust
CsI radioactivity negligible for < mphotocathode.
Commercial:V ~ 10 kV in < 1 s.
Preliminary tests encouraging.
S1
S1
S2
S3
S4
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For a large-scale experiment
Purification in liquid phase - sparkpurifier
CsI photocathode
Charge-gain readout
High quality x-y reconstruction.Especially lack of tails.
Radioactivity
Cost Gas gain of > 1000 needed.
Measured gain, 175 K.
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