Transcript Document 7308140

Searching for Double Beta Decay with EXO-200
Carter Hall (SLAC)
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A liquid xenon TPC as a 0 detector
•Monolithic TPC design has optimal surface area to volume ratio
•Full three dimensional event reconstruction
•Fluid can be purified in situ
•Noble gas isotope enrichment relatively easy and safe
•No crystal growth
•No long-lived xenon isotopes to activate
but
•Energy resolution modest compared to 76Ge & 130Te
•Experimental technique less mature
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Xenon can be continuously purified
of chemical and radioactive contaminants
Two gamma lines
from 207Bi
Fluids often have
extraordinarily low
radioactivity, and noble
gases are particularly
simple to purify.
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SLAC Xenon Purity Monitor
anode
To measure the
electron lifetime:
FET charge sensitive
preamp and shaper
drift region
grids
•~106 photoelectric
electrons produced by
laser
•initial charge measured
at photocathode
•electrons drift through
11 cm of LXe
laser
photocathode
•final charge measured by
anode
Purpose: develop procedures for achieving and maintaining high LXe purity, and
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test proposed detector materials for outgassing and poisoning properties.
SLAC Xenon Purity Monitor
SAES purifier
Cooling loop
from Polycold
refrigerator
Xenon supply
purity monitor
cryostat filled
with HFE
recirculation pump
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Outgassing tests with detector materials
Outgassing poisons the LXe, but stops after several weeks.
Re-circulation recovers the purity.
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Liquid xenon calorimetry
Measure the event energy by collecting the ionization on the anode
and/or observing the scintillation.
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Liquid xenon data show an anti-correlation
between ionization and scintillation
1 kV/cm
~570 keV
Bi-207 source
Energy resolution: 3.0% @ 570 keV or 1.4 % @ Q()
Factor of two better than most recent Xe 0 experiment
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The crown jewels of EXO
200 kg of xenon enriched to 80% in 136Xe:
the most isotope in possession by any 0 collaboration.
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EXO-200: the first 200 kg 0 experiment
Copper liquid
xenon vessel
HFE-7000 cryofluid
copper cryostat
lead shielding
200 kg of Liquid Xenon to be contained in low background
copper vessel, surrounded by 50 cm of ultra pure cryofluid
inside a copper cryostat and shielded by 25 cm of lead.
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Copper LXe vessel design is
nearly finalized...
fabrication will begin soon
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Crossed wire planes and APD array
measure event energy and position
y-position given by induction signal on shielding grid.
x-position and energy given by charge collection grid.
APD array observes prompt scintillation to measure drift time.
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EXO-200 dual TPC
cathode
crossed wire
planes and avalanche
photodiodes
charge drift direction
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field shaping rings
Hexagonal Wire Grids and APD array
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Cabling of APD array
Cable routing is tricky...
Space must be minimized
to conserved enriched xenon
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paper mock-up of cabling scheme
TPC wire grids produced by photoetching
Charge collection with
photoetched wire grids
Wires connected in
gangs-of-three to reduce
channel count
Wire
-grid closeup
Wire-grid
closeup
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Scintillation detected by Avalanche Photodiodes
Gang-of-seven APDs
EXO-200 will have 518 APDs
Triply redundant electrical
connections made by
photoetched “spider”
Sensitive area is 16 mm in diameter
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Assembly of EXO-200 lead shield
in the EXO cleanrooms at Stanford began last month
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Installation of EXO-200
cryostat at Stanford:
May 25-28 2006
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EXO-200 xenon handling
and cryogenics
refrigerators
Xenon purification
system
xenon gas
compressors
Crane for assembling
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lead arches
EXO-200 Electronics designed and built at SLAC
Front-end board
Trigger module
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EXO-200 will move in November 2006 to WIPP
in Carlsbad, NM for physics data taking.
EXO-200 clean rooms
at Stanford
EXO-200 cavern
The EXO cavern
underground
at WIPP
underground at WIPP
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Sensitivity of EXO-200
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)
(eV)
6.4*1025
QRPA (NSM)
0.18
(0.53)
Improves on previous 136Xe experiments by one order-of-magnitude,
and competitive with the best 0 experiments in the world.
EXO-200 will also make the first observation of 2 in Xe-136.
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SLAC is contributing to nearly all aspects of EXO-200:
• Mechanical design of detector and LXe vessel
• Electronics and DAQ
• Cryogenics, refrigeration, and HFE handling
• Xenon handling and purification
• Slow controls and monitoring
• APD testing and UV reflectance measurements
• Outgassing tests with the xenon purity monitor
• Detector simulation and event reconstruction software
• Computer networking and data handling
• Installation at Stanford and WIPP
• High voltage feedthrus
• Cleanroom UPS
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ITEP
ИТЭФ
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