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High-Pressure Gaseous Xenon TPC for 0- v  Search in 136 Xe

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

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High-Pressure Gaseous Xenon TPC for 0- v  Search in 136 Xe

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  1. High-Pressure Gaseous Xenon TPCfor 0-v Search in 136Xe Azriel Goldschmidt, Tom Miller, David Nygren, Josh Renner, Derek Shuman, Helmuth Spieler, Jim Siegrist LBNL 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 energyand 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 NEXTCollaboration, now preparing for a 100 kg 136Xe TPC detector for Canfranc Underground Laboratory, Spain. NEXT is funded by Spain at ~5M € for construction Spain-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! Large fluctuations between light/charge WIMPs: S2/S1 suffers! Ionization signal only Here, the fluctuations are normal For  <0.55 g/cm3, ionization energy resolution is “intrinsic” TIPP 2011

  5. Intrinsic energy resolution E/E = 2.35  (FW/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 electrons N =(FN)1/2~63 electrons rms! TIPP 2011

  6. Intrinsic energy resolution E/E = 2.35  (FW/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 electrons N =(FN)1/2~124 electrons rms! TIPP 2011

  7. Gain and noise Impose 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: GasProportional 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 noise F  constraint due to fixed energy deposit = 0.15 Let “G” represent noise/fluctuations in EL gain Uncorrelated 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 electron G  1.5/Npe Npe > 10 per electron for G ≤ F E/E = 0.9% FWHM 137Cs 662 keV TIPP 2011 9

  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 19 PMTs and PMT bases Electroluminescence region10 kV across a 3 mm gap 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 Primary Scintillation (S1) T0 of event Electroluminescence (S2) Structure indicates topology due to Compton scatters Drift Time:z-position (~0.01mm/sample) TIPP 2011 10ns/sample

  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 Counts keV TIPP 2011

  23. HPXe @ 10 Atm, 137Cs 662 keV Drift Time and Position corrections applied 1.8% FWHM Counts 29-36 keV Xe x-rays escape keV 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! TIPP 2011

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