Current Status of The EXO-200
Experiment
136Xe
136Ba++
+ 2e- (+ 2νe)
Kevin O’Sullivan
Stanford University
TeVPA 2009
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Why use xenon?
Energy resolution is poorer than the crystalline devices (~factor 10), but
Xenon isotopic enrichment is easier. 200kg of Xe has already been enriched
to 80% in 136Xe
Xenon is “reusable”.
Monolithic detector.
Can be repurified & recycled into new detector
LXe is self shielding, surface contamination minimized.
Minimal cosmogenic activation.
No long lived radioactive isotopes of Xe.
… admits a novel coincidence technique. Background reduction by Ba
daughter tagging.
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Ba Ion Identification
• Ba+ system well studied
(Neuhauser, Hohenstatt, Toshek,
Dehmelt 1980)
• Very specific signature:
“shelving”
• Single ions can be detected
from a photon rate of 107/s
6P1/2
650nm
493nm
Metastable 47s
• Important additional
constraint
• Drastic background
reduction
5D3/2
6S1/2
TeVPA 2009
GR = 5.28 MHz
GB = 15.2 MHz
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Paths to a Ton Scale Experiment
• EXO-200
– Low-background Xe TPC with 200kg of 80% enriched 136Xe
– No Ba Tagging
• Liquid Phase Barium Tagging
– Ion transfer from LXe to ion trap
– Ba tagging in Situ
– Ba tagging in SXe
• Gas Phase R&D
– ~100kg prototype detectors
– Ion manipulation in gas
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EXO-200
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Improving the Energy Resolution
Ionization and Scintillation
results using 207Bi
~570 keV
Ionization alone:
σ(E)/E = 3.8% @ 570 keV
or 1.8% @ Qββ
Ionization & Scintillation:
σ(E)/E = 3.0% @ 570 keV
or 1.4% @ Qββ
E.Conti et al. Phys. Rev. B (68)
054201
EXO-200 will collect 3-4
times
as much scintillation…
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Central HV plane
(photo-etched
phosphor bronze)
acrylic
supports
LAAPD plane (copper) and x-y wires
(photo-etched phosphor bronze)
teflon light reflectors
field shaping rings
(copper)
flex cables on back
of APD plane (copper
on kapton)
x-y crossed
wires, 60o
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EXO-200 Copper Chamber
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The EXO-200 detector
Refrigeration
feedthroughs
class 100
clean room
The Xe vessel
Vacuum
insulation
HFE feedthrough
Vacuum pump-out
port
HFE (Heat
transfer fluid)
25cm enclosure
of low activity
TeVPA 2009lead
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Materials qualification database
• Neutron Activation Analysis (NAA) - Alabama (MIT reactor)
• ICP-MS and GD-MS - INMS (Ottawa), commercial outfits
• Radon emanation - Laurentian (Sudbury)
• Gamma counting - Neuchâtel, Alabama
• Alpha counting - Alabama, Carleton, SLAC, Stanford
• Monte Carlo
~ 330 entries
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Xenon Handling System
xenon condenser
xenon purity
monitor and heater
EXO-200 goal: 0.1 ppb O2 equivalent
t ~ 4 ms (electrons)
muon flux at WIPP
(~ 1700 m.w.e.):
-3
-2 -1
4.77×10 m s
-3 -2 -1 -1
(3.10×10 m s sr ,
-2 -1
~15 m h )
EXO-200
E.-I.Esch et al.,
Nucl. Instr. Meth. A 538(2005)516
★
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EXO-200 Majorana mass sensitivity
Assumptions:
1) 200kg of Xe enriched to 80% in 136
2) σ(E)/E = 1.4% obtained in EXO R&D, Conti et al., Phys Rev B 68 (2003) 054201
3) Low but finite radioactive background: 20 events/year in the ±2σ interval centered
around the 2457.9(0.4) keV endpoint 1
5) Negligible background from 2nbb (T1/2>1·1022yr) 2
Case
Mass Eff.
(ton)
(%)
Run
Time
(yr)
EXO-200
0.2
70
2
σE/E @ Radioactive
2.5MeV Background
(%)
(events)
1.6*
40
T1/20ν
Majorana mass
(yr,
90%CL)
(meV)
6.4*1025
QRPA3 NSM4
133
186
1) M. Redshaw, J., McDaniel, E. Wingfield and E.G. Myers (Florida State
Precision Penning Trap), to be submitted to Phys. Rev C.
2) R. Bernabei et al., Phys. Lett. B 546, 23 (2002)
3) Rodin, et. al., Nucl. Phys. A 793 (2007) 213-215
4) Caurier, Phys. Rev. Lett. 100, 052503 (2008)
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Future Plans
• All EXO-200 infrastructure is underground
undergoing final testing
• The LXe TPC is built
• Electronics testing underway
• The TPC is scheduled to be installed in the
cryostat before the end of 2009
• Running will start next year with natural Xenon
with an eventual switch to enriched Xenon
• Ba Tagging and gas phase R&D ongoing
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Enriched Xenon Observatory
for double beta decay
K.Barry, E.Niner, A.Piepke
Physics Dept, U. of Alabama, Tuscaloosa Al
P.Vogel
Physics Dept Caltech, Pasadena Ca
M.Dixit, K.Graham, C.Green, C.Hagemann, C.Hargrove, E.Rollin, D.Sinclair, V.Strickland
Carleton University, Ottawa, Canada
C. Benitez-Medina, S.Cook, W.Fairbank Jr., K.Hall, B.Mong
Colorado State U., Fort Collins Co
M.Moe Physics
Dept UC Irvine, Irvine Ca
D.Akimov, I.Alexandrov, A.Burenkov, M.Danilov, A.Dolgolenko, A,Karelin, A.Kovalenko, A.Kuchenkov,
V.Stekhanov, O.Zeldovich
ITEP Moscow, Russia
B.Aharmim, K.Donato, J.Farine, D.Hallman, U.Wichoski
Laurentian U., Sudbury, Canada
H.Breuer, C.Hall, L.Kaufman, D.Leonard, S. Slutsky, Y-R. Yen
U. of Maryland, College Park Md
K.Kumar, A.Pocar
U. of Massachusetts, Amherst Ma
M.Auger, G.Giroux, R.Gornea, F.Juget, G.Lutter, J-L.Vuilleumier, J-M.Vuilleumier
Laboratory for High Energy Physics, Bern, Switzerland
N.Ackerman, M.Breidenbach, R.Conley, W.Craddock, S. Herrin, J.Hodgson, D.McKay, A.Odian, C.Prescott,
P.Rowson, K.Skarpaas, K.Wamba, J.Wodin, L.Yang, S.Zalog
SLAC, Menlo Park CA
L.Bartoszek, R.DeVoe, M.Dolinski, P.Fierlinger, B.Flatt, G.Gratta, M.Green, F.LePort, M.Montero-Diez,
R.Neilson,
TeVPA
2009A.Reimer-Müller, A.Rivas, K.O’Sullivan, K.Twelker
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Stanford University, Stanford, Ca
Back up Slides
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Xenon Enrichment
Total of 200kg of Xe enriched
to 80% in 136Xe
Natural
Xe
Enriched
Xe
EXO
Stockpile
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Ba Tagging
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Ba+ Tagging Schematic for EXO
Ba+
grabber
Quadrupole linear
ion trap
e-
e-
ee- ee-
CCD
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Single Ba ion trapping
RF quadrupole potential in each segment
Multiply by 16, and add a buffer gas to cool
down the ions injected at one end of the
trap into a DC minimum
Ba oven
e-gun
Fluorescence
imaging
...
longitudinal
trapping
0V
-10 V
short longitudinal
trapping segment
radial
trapping
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Detection of Single Ions in
Buffer Gas
2
1
ion ions
Single ion cloud
(5 s integration)
0 ions
1
ion
2
ions
0
ions
10-3 Torr He
P(493) = 75 μW
P(650) = 300 μW
Electrodes glowing from
scattered laser light
3
ions
3
ions
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M. Green, et al. Phys. Rev. A 76 023404
(2007)
Capacitive cryo-tip
2 mm
Electrostatic
field lines
Cryo-tip (ground)
1 mm
Picture of sensor
Capacitive
sensor (-HV)
from LXe
Ion mobility: µ ~ 0.3 cm2/kVs
v = µ x 1kV/cm ~ 0.3 cm/s
K. Wamba et al., NIM A 555 (2005) 205
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Full EXO Sensitivity
Assumptions:
1) 80% enrichment in 136
2) Intrinsic low background + Ba tagging eliminate all radioactive background
3) Energy res only used to separate the 0ν from 2ν modes:
Select 0ν events in a ±2σ interval centered around the 2457.9(0.4) keV endpoint1
4) Use for 2νββ T1/2>1·1022yr2
Case
Mass Eff.
(ton)
(%)
Run σE/E @
2νββ
Time 2.5MeV Background
(yr)
(%)
(events)
Conservative
1
70
5
1.6*
Aggressive
10
70
10
1†
0.5 (use 1)
T1/20ν
Majorana mass
(yr,
90%CL)
(meV)
2*1027
0.7 (use 1) 4.1*1028
QRPA3 NSM4
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33
5.3
7.3
1) M. Redshaw, J., McDaniel, E. Wingfield and E.G. Myers (Florida State Precision
Penning Trap), to be submitted to Phys. Rev C.
2) R. Bernabei et al., Phys. Lett. B 546, 23 (2002)
3) Rodin, et. al., Nucl. Phys. A 793 (2007) 213-215
4) Caurier, Phys. Rev. Lett. 100, 052503 (2008)
TeVPA 2009
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