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D.Leonard, A.Piepke Physics Dept, University of Alabama, Tuscaloosa AL

E nriched X enon O bservatory for double beta decay. D.Leonard, A.Piepke Physics Dept, University of Alabama, Tuscaloosa AL P.Vogel Physics Dept Caltech, Pasadena CA A.Bellerive, M.Bowcock, M.Dixit, I. Ekchtout, C.Hargrove, D.Sinclair, V.Strickland

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D.Leonard, A.Piepke Physics Dept, University of Alabama, Tuscaloosa AL

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  1. Enriched Xenon Observatoryfor double beta decay D.Leonard, A.Piepke Physics Dept, University of Alabama, Tuscaloosa AL P.Vogel Physics Dept Caltech, Pasadena CA A.Bellerive, M.Bowcock, M.Dixit, I.Ekchtout, C.Hargrove, D.Sinclair, V.Strickland Carleton University, Ottawa, Canada W.Fairbank Jr., S.Jeng, K.Hall Colorado State University, Fort Collins CO M.Moe Physics Dept UC Irvine, Irvine CA D.Akimov, A.Burenkov, M.Danilov, A.Dolgolenko, A.Kovalenko, D.Kovalenko, G.Smirnov, V.Stekhanov ITEP Moscow, Russia J.Farine, D.Hallman, C.Virtue Laurentian University, Canada M.Hauger, F.Juget, L.Ounalli, D.Schenker, J-L.Vuilleumier, J-M.Vuilleumier, P.Weber Physics Dept University of Neuchatel, Switzerland M.Breidenbach, R.Conley, C.Hall, D.McKay, A.Odian, C.Prescott, P.Rowson, J.Sevilla, K.Skarpaas, K.Wamba SLAC, Menlo Park CA R.DeVoe, B.Flatt, G.Gratta, M.Green, F.LePort, R.Neilson, A.Pocar, S.Waldman, J.Wodin Physics Dept Stanford University, Stanford CA EXO SLAC DOE Pgm Rev M. Breidenbach

  2. Outline • Why EXO • EXO 200 Description, Capabilities and Status • SLAC Personnel • EXO 200 Progress Carter Hall Breakout • Ba Tagging R&D Peter Rowson Breakout EXO SLAC DOE Pgm Rev M. Breidenbach

  3. Main challenge in 0νββ decay 1) Very large fiducial mass (tons) need large-scale isotopic enrichment 2) Reduce and control backgrounds in qualitatively new ways existing experiments are already background limited, unlikely to gain big factors without new techniques For no background For a background scaling like Nt Need 2) to fully utilize 1) and make a worthwhile experiment EXO SLAC DOE Pgm Rev M. Breidenbach

  4. ββdecay experiments are at the leading edge of “low background” techniques • Final state ID: 1) “Geochemical”: search for an abnormal abundance • of (A,Z+2) in a material containing (A,Z) • 2) “Radiochemical”: store in a mine some material (A,Z) • and after some time try to find (A,Z+2) in it • + Very specific signature • + Large live times [particularly for 1)] • + Large fiducial masses • - Possible only for a few isotopes [in the case of 1)] • - No distinction between 0ν, 2νor other modes • “Real time”: ionization or scintillation is detected in the decay • a) “Homogeneous”: source=detector • b) “Heterogeneous”: source≠detector • + Energy/some tracking available [can distinguish modes] • + In principle universal (b) • - Many γ backgrounds can fake signature • - Exposure is limited by human patience EXO is designed to combine these two techniques for a uncontroversial result EXO SLAC DOE Pgm Rev M. Breidenbach

  5. Xe is ideal for a large experiment • No need to grow crystals • Can be re-purified during the experiment • No long lived Xe isotopes to activate • Can be easily transferred from one detector to • another if new technologies become available • Noble gas: easy(er) to purify • 136Xe enrichment easier and safer: • - noble gas (no chemistry involved) • - centrifuge feed rate in gram/s, all mass useful • - centrifuge efficiency ~Δm. For Xe 4.7 amu • 129Xe is a hyperpolarizable nucleus recently FDA approved for lung NMR • tomography… a joint enrichment program ? EXO SLAC DOE Pgm Rev M. Breidenbach

  6. 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 metastable 47s 4D3/2 • Important additional • constraint • Huge background • reduction 2S1/2 EXO SLAC DOE Pgm Rev M. Breidenbach

  7. The Ba-tagging, added to the Xe TPC rejection Power, provides the tools to develop a background-free next-generation ββ experiment Energy resolution is still the all-important parameter to separate the 0nbb mode from 2nbb EXO fiducial mass between 1 and 10 tons, of 136Xe at 80% depending on the status of the field when we finalize the design EXO SLAC DOE Pgm Rev M. Breidenbach

  8. Conceptual scheme of a large LXe detector with Ba extraction EXO SLAC DOE Pgm Rev M. Breidenbach

  9. The roadmap to the background free discovery of Majorana neutrinos and the neutrino mass scale Learn about physics and economics of Xe enrichment on a grand scale Improve the energy resolution in LXe Gain practice with Ba trapping and spectroscopy in Xe and other gases Gain practice with Ba grabbing and release Design & build a large size, low background prototype LXe 0νββ detector Enrich a large amount of Xe (200 kg) Measure 2νββ in 136Xe, gain operational experience, reach the best 0νββ sensitivity Build a fully functional ion grab, transfer, trap, spectroscopy cell Investigate direct tagging in LXe Done In progress To do Design and build a large, ton scale experiment with Ba tagging EXO SLAC DOE Pgm Rev M. Breidenbach

  10. 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 = 1.4% 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 ‡ Rodin et al Phys Rev C 68 (2003) 044302 # Courier et al. Nucl Phys A 654 (1999) 973c EXO SLAC DOE Pgm Rev M. Breidenbach

  11. EXO-200: an intermediate detector without Ba tagging • Need to test detector technology, particularly the LXe option: • A 200 kg chamber is close to the largest Xe detector ever built • and hence good training ground • Essential to understand backgrounds from radioactivity: • 200 kg is the minimum size for which the self-shielding is • important and there is negligible surface inefficiency • Using 136Xe can hope to measure the “background” 2nbb mode: • 200 kg is needed to have a chance (if do not see the mode then • is really good news for the large experiment !!) • The production logistics and quality of 136Xe need to be tested: • Need a reasonably large quantity to test production • Already a respectable (20x) bb decay experiment • No need for Ba tagging at this scale EXO SLAC DOE Pgm Rev M. Breidenbach

  12. EXO-200kg Majorana mass sensitivity • Assumptions: • 200kg of Xe enriched to 80% in 136 • σ(E)/E = 1.4% obtained in EXO R&D, Conti et al Phys Rev B 68 (2003) 054201 • Low but finite radioactive background: • 20 events/year in the ±2σ interval centered around the 2.481MeV endpoint • 4) Negligible background from 2νββ (T1/2>1·1022yr R.Bernabei et al. measurement) † Rodin et al Phys Rev C 68 (2003) 044302 ♦ Courier et al. Nucl Phys A 654 (1999) 973c • What if Klapdor’s observation is correct ? • Central value T1/2 (Ge) = 1.2+3-0.5 ·1025, ±3σ range (0.24eV – 0.58eV) • (Phys. Lett. B 586 (2004) 198-212) • In 200kg EXO, 2yr: • Worst case (QRPA, upper limit) 15 events on top of 40 events bkgd  2σ • Best case (NSM, lower limit) 162 events with 40 bkgd  8.5σ EXO SLAC DOE Pgm Rev M. Breidenbach

  13. 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. EXO-200 should definitely resolve this issue EXO SLAC DOE Pgm Rev M. Breidenbach

  14. 200 kg 136Xe test production completed in spring ’03 (80% enrichment) • Largest highly enriched stockpile • not related to nuclear industry • Largest sample of separated ββ • isotope (by ~factor of 10) EXO SLAC DOE Pgm Rev M. Breidenbach

  15. EXO-200: a 200kg LXe TPC with scintillation readout in a ultra-low background cryostat/shielding Heat exchange/shielding fluid ~1.7m 200 kg chamber Ultra-low activity copper EXO SLAC DOE Pgm Rev M. Breidenbach

  16. EXO-200 Xe handling and purification system ready in cleanroom electronics rack SAES Zr purifier valves and instrumentation manifold RGA turbo pump Recovery compressors due for delivery in Jun 05 EXO SLAC DOE Pgm Rev M. Breidenbach

  17. Recirculation essential EXO-200 goal l > 400 cm t ~ 4 ms 0.1 ppb O2 equivalent Conclusion: common impurities (O2, H2O, CO2) efficiently removed by purifier, recirculation. EXO SLAC DOE Pgm Rev M. Breidenbach

  18. EXO R&D showed the way to improved energy resolution in LXe: Use (anti)correlations between ionization and scintillation signals 1 kV/cm ~570 keV EXO SLAC DOE Pgm Rev M. Breidenbach

  19. Anti-correlated ionization and scintillation improves the energy resolution in LXe Ionization alone: σ(E)/E = 3.8% @ 570 keV or 1.8% @ Qββ Compilation of Xe resolution results Ionization & Scintillation: σ(E)/E = 3.0% @ 570 keV or 1.4% @ Qββ (a factor of 2 better than the Gotthard TPC) EXO ioniz only E.Conti et al. Phys. Rev. B: 68 054201 EXO ioniz + scint EXO-200 will collect 3-4 times as much scintillation… further improvement possible EXO SLAC DOE Pgm Rev M. Breidenbach

  20. EXO-200 TPC basics • The detector measures both the ionization electrons and the scintillation light to get best energy resolution. • In addition, the position of the decay is measured to get spatial distributions and (for later) the position of the Ba ion. • Info on event topology also important for background separation. • The detector is a cylinder of 44 cm ID by 44 cm inner length. • The cylinder is split by a cathode plane at the center so there are two symmetric drift regions. The cathode runs at negative HV. • Max HV is ~ 70kV (~3.5 kV/cm drift). Energy resolution improves with drift field, but there are arguments that separation of 1 vs 2 primary electrons might be better at lower fields.  field optimization is an important mission of EXO-200 • Readout “style”: • Crossed wires, 100μm wires, 3mm pitch, ganged in groups of 3 48ch x, 48ch y, total 96 ch per 1/2 detector (Pad readout rejected because of high channel count) EXO SLAC DOE Pgm Rev M. Breidenbach

  21. EXO SLAC DOE Pgm Rev M. Breidenbach

  22. Unmounted LAAPD from Advanced Photonix Special gold-less production for us APDs are ideal for our application: - very clean & light-weight, - very sensitive to VUV QE > 1 at 175nm Gain set at 100-150 V~1500V ΔV < ±0.5V ΔT < ±1K APD is the driver for temperature stability Leakage current OK cold Channel count: 2*300

  23. Teflon vessel • In engineering phase • Teflon has advantages: - ultra-low activity - LXe compatible - Good VUV reflector • Teflon has disadvantages: - relatively weak plastic - large, non-uniform CTE • Weld everything together: - minimize materials - automatically match CTE • PFA and some very special PTFE can be welded (with some effort) • Standard technique involves re-baking of part • Special “fusion” clamp technology being developed under DoE SBIR-I with APT. Excellent progress being made: we have ionization and scintillation detected in a “all teflon” chamber. This is a (technical) first ! • “Can opener” has to be designed EXO SLAC DOE Pgm Rev M. Breidenbach

  24. Welded test chamber uses the same grid/APDs structure just tested EXO SLAC DOE Pgm Rev M. Breidenbach

  25. 4 “all teflon” vessels built: all He-leak tested OK • Body made out of parts • sintered and fused in • the oven • Recirculation pipes • preformed and welded • with hot clamp • Large seal welded with • hot clamp One vessel contains a fully functional ionization AND scintillation detector EXO SLAC DOE Pgm Rev M. Breidenbach

  26. Electronics nearly ready: final (small) mods on front end boards following review on Jun 6, 2005 Front-end board Trigger module EXO SLAC DOE Pgm Rev M. Breidenbach

  27. Modular clean rooms at Stanford EXO SLAC DOE Pgm Rev M. Breidenbach

  28. Massive effort on material radioactive qualification using: • NAA (MIT-Alabama) • Low background γ-spectroscopy (Neuchatel, Alabama) • α- counting (Alabama, Stanford, SLAC, Carleton) • Radon counting (Laurentian) • High performance GD-MS and ICP-MS • (Commercial, Canadian Inst. Standards) • At present the database of characterized materials • includes 77 entries • MC simulation of backgrounds at • Alabama and Stanford/SLAC • The impact of every screw within the Pb shielding is evaluated • before acceptance EXO SLAC DOE Pgm Rev M. Breidenbach

  29. Modules arrive here and are transferred to WIPP flatcar. Flatcar is moved to waste handling shaft and lowered into mine. Flatcar load rating: 67,000 lbs. EXO-200 at WIPP Modules are then moved to NExA and placed in position and connected. Distance traveled ~ 2100 ft. EXO SLAC DOE Pgm Rev M. Breidenbach

  30. EXO-200 home underground: (NExA) EXO SLAC DOE Pgm Rev M. Breidenbach

  31. Personnel • Physicists: M.Breidenbach, C.Hall, D.McKay, A.Odian, C.Prescott, P.Rowson, K.Wamba • Engineers: J.Sevilla, K.Skarpaas, D. Freytag, R. Herbst, J. Hodgson • Techs: R.Conley, P. Tung • Admins: N. Haulman • FTES (FY05): • Physicists (Profs + Perm Staff) 2.7 • Physicists (Post-docs) 0.9 • Physicists (Students) 0.9 • Engineers (Mech) 1.4 • Engineers (Electronic) 0.7 • Techs 1.2 • Admin 0.1 • Other 0.1 • Total 8.1 EXO SLAC DOE Pgm Rev M. Breidenbach

  32. SLAC Involvement • EXO is a small, very collaborative organization. • SLAC is involved in all aspects of EXO except: • Laser tagging of extracted Ba (but very involved in the extraction) • Laser tagging of Ba in the bulk Xe • Radiopurity measurements (except for GDMS techniques) EXO SLAC DOE Pgm Rev M. Breidenbach

  33. Conclusions EXO-200 very soon will be ready • Largest double beta decay detector ever • Largest amount of separated isotope (by a factor of 10) in hand • Tie for the largest Xe detector ever… • But we are - ultra-clean • - enriched xenon • First liquid bath cooled/shielded LXe detector • First Ionization & Scintillation LXe detector • First massive use of APDs for scintillation readout • First teflon detector vessel EXO SLAC DOE Pgm Rev M. Breidenbach

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