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EXO-GAS Detector

EXO-GAS Detector. Status report for the SNOLAB EAC August 2007. EXO Canada Team. Laurentian J. Farine, D. Hallman, C. Virtue, U. Wichoski Adam Blais (Summer Student) Carleton M. Dixit, K. Graham, C. Hargrove, D. Sinclair C. Green, E. Rollin (Grad. Students)

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EXO-GAS Detector

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  1. EXO-GAS Detector Status report for the SNOLAB EAC August 2007

  2. EXO Canada Team • Laurentian • J. Farine, D. Hallman, C. Virtue, U. Wichoski • Adam Blais (Summer Student) • Carleton • M. Dixit, K. Graham, C. Hargrove, D. Sinclair • C. Green, E. Rollin (Grad. Students) • K. McFarlane (Engineer) L. Anselmo (Chemist)

  3. Heidelberg-Moscow Results for Ge double beta decay 57 kg years of 76Ge data Apply single site criterion

  4. Normal and Inverted Mass Hierarchies

  5. We need to develop new strategies to eliminate backgrounds to probe the allowed space Inverted Barium tagging may offer a way forward Normal

  6. EXO – Enriched Xenon Observatory • Look for neutrino-less double beta decay in Xe • 136Xe --- 136Ba + e- + e- • Attempt to detect ionization and the Ba daughter • Ba is produced as ++ ion • Ba+ has 1 electron outside Xe closed shell so has simple ‘hydrogenic’ states • Ba++ can (?) be converted to Ba+ with suitable additive

  7. Advantages of Xe • Like most noble gases/liquids it can be made extremely pure • No long lived radioactive isotopes • High Q value gives favourable rates • Readily made into a detector • Possible barium tagging to eliminate backgrounds

  8. Liquid or Gas Liquid Compact detector No pressure vessel Small shield -> lower purity reqd. Gas Energy resolution Tracking & multi-site rejection In-situ Ba tagging Large detector Needs very large shield Pressure vessel is massive Large Cryostat Poorer energy, tracking resolution Ex-situ Ba tagging

  9. Liquid Detector EXO 200 • Objectives • Prove the liquid detection concept • Measure bb2n decay rate for Xe • Test the HM claim for observation of bb0n • Under construction at Stanford for deployment at WIPP • Major engineering support from Vance Strickland

  10. Status of 2ν mode in 136Xe 2νββ decay has never been observed in 136Xe. Some of the lower limits on its half life are close to (and in one case below) the theoretical expectation. The 200kg EXO prototype should definitely resolve this issue

  11. EXO neutrino effective mass sensitivity • Assumptions: • 80% enrichment in 136 • Intrinsic low background + Ba tagging eliminate all radioactive background • Energy res only used to separate the 0ν from 2ν modes: • Select 0ν events in a ±2σ interval centered around the 2.481MeV endpoint • 4) Use for 2νββ T1/2>1·1022yr (Bernabei et al. measurement) *s(E)/E = 1.6% obtained in EXO R&D, Conti et al Phys Rev B 68 (2003) 054201 †s(E)/E = 1.0% considered as an aggressive but realistic guess with large light collection area ‡ QRPA: A.Staudt et al. Europhys. Lett.13 (1990) 31; Phys. Lett. B268 (1991) 312 # NSM: E.Caurier et al. Phys Rev Lett 77 (1996) 1954

  12. Xe offers a qualitatively new tool against background: 136Xe 136Ba++ e- e- final state can be identified using optical spectroscopy (M.Moe PRC44 (1991) 931) Ba+ system best studied (Neuhauser, Hohenstatt, Toshek, Dehmelt 1980) Very specific signature “shelving” Single ions can be detected from a photon rate of 107/s 2P1/2 650nm 493nm 4D3/2 • Important additional • constraint • Huge background • reduction metastable 80s 2S1/2

  13. Possible concept for a gas double beta counter Anode Pads Micro-megas WLS Bar Electrode Xe Gas Lasers . . . . . . . . . . . . . . . . Grids PMT For 200 kg, 10 bar, box is 1.5 m on a side

  14. Possible concept for a gas double beta counter Anode Pads Micro-megas WLS Bar Xe Gas Isobutane TEA Electrode Lasers . . . . . . . . . . . . . . . . Grids PMT For 200 kg, 10 bar, box is 1.5 m on a side

  15. Triggers • Level 1 • Light => event in fiducial volume • Light => energy = Q +- 10% • Level 2 • Ionization => energy = Q +- 3% • 2 Bragg peaks • Single site event • Determine Ba location • Start search for Ba

  16. Gas Option for EXO • Need to demonstrate good energy resolution (<1% to completely exclude bb2n ) tracking, • Need to demonstrate Ba tagging • Deal with pressure broadening • Ba ion lifetime • Ba++ -> Ba+ conversion • Can we cope with background of scattered light

  17. Tasks to design gas EXO • 1) Gas Choice • Measure Energy resolution for chosen gas • (Should be as good as Ge but this has never been achieved) • Measure gain for chosen gas • Measure electron attachment for chosen gas • Understand optical properties • Measure Ba++ -> Ba+ conversion • Measure Ba+ lifetime

  18. Tasks to design EXO Gas • 2) TPC Design • What pressure to use • What anode geometry to use • What chamber geometry to use • What gain mechanism to use • Develop MC for the detector • Design electronics/DAQ

  19. Tasks to design EXO Gas • 3) Ba Tagging • Demonstrate single ion counting • Understand pressure broadening/shift • Understand backgrounds • Fix concept

  20. Tasks to design EXO Gas • 4) Overall Detector concept • Fix shielding requirements and concepts • Design pressure containment • Fix overall layout

  21. Gas Properties • Possible gas – Xe + iso-butane + TEA • Iso-butane to keep electrons cold, stabilize micromegas/GEM • TEA • Converts Ba++ -> Ba+ • Q for TEA + Ba++->TEA+ + Ba+* ~ 0 • Converts 172 nm -> 280 nm? • ? Does it trap electrons? • ?Does it trap Ba+?

  22. Measuring Gas properties • Gridded ion chamber being used to measure resolution, drift of electrons using alpha source

  23. Movable source holder Contacts rings with wiper Field Rings Source Grid Anode Gridded Ion Chamber

  24. Progress on energy resolution – Pure Xe, 2 Bar s = 0.6% Alpha spectrum at 2 b pressure.

  25. Energy Spectrum for Xe + CH4 (5%)

  26. Xe + 5% CH4

  27. Note: (1) peak width was constant at ~0.6% over the range (2) Gas was not purified but was spec’d at 99.9%

  28. Current status on energy resolution • Ionization in gaseous Xe gives adequate energy resolution, even for alpha particles. • We can now use this to explore gain options

  29. Studying Ba ions in high pressure Xe gas Thin (5 mm) Pt wire + Ba Grid 1 - - - - - - - - - - - - - - - - - - __ __ __ __ __ __ __ __ __ __ __ __ __ Laser Beams - - - - - - - - - - - - - - - - - - Grid 2 Filter PMT Pulseredandbluelasers out of phase with each other

  30. Ion production in test cell (detection using Channeltron)

  31. Progress on Ba tagging

  32. Problems with Proposed technique • It appears that the D state de-excites through collisions on a timescale short compared to our laser pulsing • This would allow a different approach • Use cw blue laser and look for red fluorescence lines • Red sensitive PMT on order

  33. Si detector 228Th Laser Beam Lens PMT Concept for single ion fluorescence of Ra

  34. Plans (Dreams) • We are working to address the technical issues associated with a large gas Xe double beta decay detector • If all goes well we will seek funding to build a 200 kg gas detector with Ba tagging

  35. EXO GAS DETECTOR CONCEPT 200 Kg Crinkled Cubic Copper Liner 3,000 lb (if 0.1 inch thick) 10.2 feet each side Acrylic Blocks 9 tonnes (Fills 25% of space) Plan View Acrylic Cylindrical Shell 14.9 feet diameter, 12.2 feet high Water Tank 28 diameter for 2 meters H2O Vacuum Around acrylic blocks ? H2O (3.3 psi + 18.2 psi) ~ 21.4 psia Water Shield 490 tonnes water If filled without internals Xe 200 kg at 18.2 psia H2O (7.7 psi + 18.2) ~ 25.9 psia Note: Decreasing the Xe pressure to 1 bar requires increasing the copper tank to 11 foot sides. Elevation

  36. Longer term plans • If things go really well we can consider a ton scale detector. • Could be either liquid or gas • If Ba tagging works very well then incentive to use separated isotope Xe is weaker • A detector of several tons could be accomodated in either the cube hall or the cryopit.

  37. EXO Progress Update Laurentian University Jacques Farine

  38. EXO Gas Option Simulation First step: containment efficiencies • Pressure and mass dependence • Cylinder, take H=2R to minimize S/V • Filled with 136Xe • Cu walls • 0 decay, Q = 2457.8 keV • Differentiate e–//both crossing fid. vol.

  39. Uncertainties obtained from 20 independent simulations. + Points include detailed low energy processes, scintillation and E=1kV/cm ( .. 30x CPU cycles).

  40. 2 / 0 differential c at edges • Simulations for 1T at 5 atm, equator • 10,000 evts ea. • Contam. of 2 in 0 increases towards the edge • > Optimize fiduc. volume and/or vary fraction of contamination

  41. Next steps • Add chemical composition / drift / attenuation / absorption / attachment // light+charge readout • Add backgrounds as source of singles • Write code to detect Bragg peaks • For single/double separation, determine: • Contamination / sacrifice • Effect of Bremsstrahlung • Light collection options > E resolution

  42. Studies related to bothL+G Options

  43. Material screening - radon emanation tests • Continued program at SNOLAB • Sensitivity 10 220Rn/day, 20 222Rn/day • Measure EXO-200 plumbing • No substantial source • Clean !

  44. Characterize counters for Ar/Xe • Allow for: • Absolute emanation measurements • Diffusion studies in • Absolute cross-calibration between gases N2 = Ar; Xe 23% lower

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