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High-Pressure Gaseous Xenon TPC for 0- v Search in 136 Xe. Azriel Goldschmidt, Tom Miller, David Nygren, Josh Renner, Derek Shuman, Helmuth Spieler, Jim Siegrist LBNL. Motivations. Xenon gas at high pressure offers excellent energy resolution - in principle - PowerPoint PPT Presentation
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TIPP 2011 1
High-Pressure Gaseous Xenon TPCfor 0-v Search in 136Xe
Azriel Goldschmidt, Tom Miller, David Nygren, Josh Renner, Derek Shuman,
Helmuth Spieler, Jim SiegristLBNL
TIPP 2011 2
Motivations• Xenon gas at high pressure offers excellent energy resolution - in principle
(within a factor 3 of best Ge diodes! )
• Electroluminescence provides linear gain with extremely low fluctuations - helps to preserve this high intrinsic energy resolution.
• HP Xe TPC can provide total energy and image of the particle tracks for topological discrimination of event type (Gotthard TPC: x30 rejection)
TIPP 2011 3
Context
• R&D is focused on the NEXT Collaboration, now preparing for a 100 kg 136Xe TPC detector for Canfranc Underground Laboratory, Spain.
NEXT is funded by Spain at ~5M € for constructionSpain-Portugal-Colombia-France-Russia-US collaboration
• Applications may include -ray imaging for Homeland security/non-proliferation, medical physics/imaging
TIPP 2011 4
Xenon: Strong dependence of energy resolution on density!
For <0.55 g/cm3, ionization energy resolution is “intrinsic”
Ionization signal onlyHere, the
fluctuations are normal
Large fluctuations
between light/charge
WIMPs: S2/S1
suffers!
TIPP 2011 5
Intrinsic energy resolutionE/E = 2.35 (FW/Q)1/2
– F Fano factor: F = 0.15 (HPXe) (LXe: F ~20)– W Average energy per ion pair: W ~ 25 eV– Q Energy deposited, e.g. 662 keV from Cs137 -rays:
E/E = 0.56% FWHM (HPXe)
N = Q/W ~26,500 primary electronsN = (FN)1/2 ~63 electrons rms!
TIPP 2011 6
Intrinsic energy resolutionE/E = 2.35 (FW/Q)1/2
– F Fano factor: F = 0.15 (HPXe) (LXe: F ~20)– W Average energy per ion pair: W ~ 25 eV– Q Energy deposited, e.g. 2457 keV from 136Xe --> 136Ba:
E/E = 0.28% FWHM (HPXe)
N = Q/W ~100,000 primary electronsN = (FN)1/2 ~124 electrons rms!
TIPP 2011 7
Gain and noiseImpose a requirement:
(noise + fluctuations) N(noise + fluctuations) 124 e—
Simple charge detection can’t meet this goal
Need gain with very low noise/fluctuations!
Electroluminescence (EL) is the key
TIPP 2011 8
Electro-Luminescence (EL) (aka: Gas Proportional Scintillation)
• Physics process generates ionization signal• Electrons drift in low electric field region• Electrons enter a high electric field region• Electrons gain energy, excite xenon: 8.32 eV• Xenon radiates VUV (175 nm, 7.5 eV)• Electron starts over, gaining energy again• Linear growth of signal with voltage• Photon generation up to ~1000/e, but no ionization• Sequential gain; no exponential growth fluctuations are very
small• NUV = JCP N1/2
• Optimal EL conditions: JCP = 0.01 (Poisson: JCP = 1)
TIPP 2011 9
Gain and noiseF constraint due to fixed energy deposit =
0.15Let “G” represent noise/fluctuations in EL
gainUncorrelated fluctuations can add in
quadrature: n = ((F + G)N)1/2
EL: G = JCP/NUV + (1 + 2PMT)2/Npe
Npe = number of photo-electrons per electronG 1.5/Npe
Npe > 10 per electron for G ≤ FE/E = 0.9% FWHM 137Cs 662 keV
TIPP 2011 10
Virtues of Electro-Luminescence in HPXe
• Linearity of gain versus pressure, HV• Immunity to microphonics• Tolerant of losses due to impurities• Absence of positive ion space charge• Absence of ageing, quenching of signal• Isotropic signal dispersion in space• Trigger, energy, and tracking functions are
accomplished with optical detectors
TIPP 2011 11
TPC with Electroluminescence: Total Energy and Track Imaging
Readout Plane A
- position
Readout Plane B- energy
Electroluminescent Layer
TIPP 2011 12
Pressure vessel design study at 15 bars for 100 kg NEXT
~120
cm
TIPP 2011 13
Laboratorio Subterraneo de Canfranc
Waiting for NEXT...
TIPP 2011 14
LBNL-TAMU TPC Prototype
TIPP 2011 15
Field cages/Light cagePTFE with copper stripes
Electroluminescence region10 kV across a 3 mm gap
19 PMTs and PMT bases
TIPP 2011 16
PMT Array: inside the pressure vesselQuartz window 2.54 cm diameter PMTs
TIPP 2011 17
Inserting the TPC...
carefully!
TIPP 2011 18
TIPP 2011 19
A Diagonal Muon Track - “reconstructed”
~ 14 cm
TIPP 2011 20
A typical 137Cs waveform (sum of 19 PMTs)~300,000 detected photoelectrons
10ns/sample
Primary Scintillation (S1)T0 of event
Electroluminescence (S2)Structure indicates topology due to Compton scatters
Drift Time:z-position (~0.01mm/sample)
TIPP 2011 21
Charge vs Drift Timeelectron lifetime of 900 ms
~5% charge loss forlongest drift of 60 ms (8 cm)
TIPP 2011 22
HPXe @ 10 Atm, 137Cs 662 keVDrift time correction applied
keV
Coun
ts
TIPP 2011 23
HPXe @ 10 Atm, 137Cs 662 keV
1.8% FWHM
29-36 keV Xe x-rays escape
keV
Coun
ts
Drift Time and Position corrections applied
TIPP 2011 24
Conclusions and Outlook• Successful operation of xenon EL TPC in 10-15 Bar range• We have achieved E/E = 1.8% FWHM @ 662 keV (10 Atm)
– If F = G, and if no other effects, we expect: E/E = 0.9% FWHM• We do not yet claim to understand this factor of 2, but...• We do expect that this gap will be substantially reduced
– Likely contributing factors:• localization - dependence of signal on radius • calibration of gain and QE of each PMT• dissociative attachment of electrons in EL region to water/oxygen• mesh flatness• PMT after-pulsing
• NEXT is starting to happen! 100 kg 136Xe awaits us!