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Thomas Koffas Stanford University

Thomas Koffas Stanford University. Z.Djurcic, D.Leonard, A.Piepke Physics Dept, University of Alabama, Tuscaloosa AL P.Vogel Physics Dept Caltech, Pasadena CA A. Bellerive, M. Dixit, C. Hargrove, D. Sinclair Carleton University, Ottawa, Canada W.Fairbank Jr., S.Jeng, K.Hall

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Thomas Koffas Stanford University

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  1. Thomas Koffas Stanford University

  2. Z.Djurcic, D.Leonard, A.Piepke Physics Dept, University of Alabama, Tuscaloosa AL P.Vogel Physics Dept Caltech, Pasadena CA A. Bellerive, M. Dixit, C. Hargrove, D. Sinclair 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, Neuchatel Switzerland M.Breidenbach, R.Conley, C.Hall, A.Odian, C.Prescott, P.Rowson, J.Sevilla, K.Skarpaas, K.Wamba, SLAC, Menlo Park CA E.Conti, R.DeVoe, G.Gratta, M.Green, T.Koffas, R.Leon, F.LePort, R.Neilson, S.Waldman, J.Wodin Physics Dept Stanford University, Stanford CA Enriched Xenon Observatoryfor double beta decay

  3. Last decade: the age of ν physics • Discovery of ν flavor change: • Solar neutrinos (MSW effect) • Reactor neutrinos (vacuum oscillation) • Atmospheric neutrinos (vacuum oscillation) • Loose ends: LSND results • So assuming that MiniBoone sees no oscillations, • we know that: • ν masses are non-zero, • There are 2.981±0.008 v (Z lineshape), • 3 ν flavors were active in Big bang Nucleosynthesis

  4. Drastically different mass scenarios are still allowed by the data 23 eV ~2.8 eV ~1 eV ~0.3 eV Time of flight from SN1987A (PDG 2002) From tritium endpoint (Maintz and Troitsk) From WMAP From 0νββ if ν is Majorana No real understanding why M so small Dirac vs Majorana neutrinos? Need a lepton number violating process…

  5.  decay can occur in two modes • Via the emission of 2’s: • A typical 2nd order nuclear process b) A neutrinoless mode: Requires both M0 and 

  6.  decay a standard but small 2nd order correction to regular  decay BUT in some cases is the only energetically allowed 2 has been observed experimentally 0 has never been observed experimentally 0 sensitive to all neutrino masses

  7. For 0 decay due to light Majorana ν masses: where, the effective Majorana neutrino mass, nuclear matrix elements that can be calculated, and a known phase-space factor, the half-life time to be measured

  8. 2 spectrum (normalized to 1) 0 peak (5% FWHM) (normalized to 10-6) 0 peak (5% FWHM) (normalized to 10-2) Summed electron energy in units of the kinematic endpoint (Q) Detection of 0νββ Decay The two e- energy sum is the primary tool from S.R. Elliott and P. Vogel, Ann.Rev.Nucl.Part.Sci. 52 (2002) 115.

  9. In a bkgnd free environment mass sensitivity scales as • If bkgnd scales like Nt mass sensitivity scales as For further substantial progress we need tons of an appropriate isotope exposed for a long time BUT there are problems Qualitatively new means are needed to suppress bkgnds and fully utilize the large fiducial mass

  10. Xe is ideal for such a measurement • It is one of the easiest isotopes to enrich; • Like argon, it represents a good ionization detecting • medium; • It exhibits substantial scintillation that can be used • to complement the ionization detection; • Can be re-purified during the experiment; • No long lived Xe isotopes to activate; • Its  decay results in 136Ba that can be identified • in its atomic form via techniques of high resolution • optical spectroscopy.

  11. 2P1/2 650nm 493nm metastable 47s 4D3/2 2S1/2 Optical detection of a 136Ba+ atom(M. Moe PRC44(1991)931) • Resonant laser detection is: • Highly sensitive, yielding >107 • photons per atom; • Highly selective; • Extensively used in the • atomic physics community. Provides additional constraint Huge bkgnd reduction probe pump

  12. Detector R&D Program • Single ion Ba+ tagging at different Xe pressures; • LXe energy resolution; • LXe purification for long e- lifetime and radioimpurities; • Ba ion lifetime and grabbing from LXe; • 136Xe Isotopic enrichment; • Procurement and characterization of low radioactivity materials; • Construction/operation of a 200kg enriched 136Xe prototype detector;

  13. EXO spectroscopy lab Ion Trap 493nm laser 650nm laser

  14. CCD Image of Ba+ ions in the trap Trap edge

  15. Millikan type experiment with the ion trap Zero ion background All above in UHV; Perform the same experiment in noble gas atmosphere

  16. Energy Resolution Measurement Setup Ionization Readout Preamplifier Reconstruct energy as linear combination of ionization and scintillation signals There are indications that correlations between the two variables help improve energy resolution;J.Seguinot et al. NIM A354 (1995) 280 1Lt Test Chamber PMT

  17. Clear anti-correlation on event-to-event basis is seen… A linear combination of ionization and scintillation WILL optimize resolution

  18. First EXO published result in Phys.Rev.B Resolution is optimized by a ~100-150 ‘mixing angle’ Ionization only 3.3%@570keV or 1.6%@2.5MeV Ionization combined with scintillation E.Conti et al Phys. Rev. B 68 (2003) 054201

  19. Xe purification studies-Continuous Xe Recirculation

  20. First 200 kg pilot production started in the Summer of 2001 and was successfully completed in May 2003 Xe leak monitoring station This is already the largest non-fissile isotope enrichment program ever entertained!

  21. 200kg 136Xe Prototype is an important step • Need to test the detector technology, particularly the LXe option; • Essential to understand backgrounds from radioactivity; • Necessary to measure the 2 “background” mode; • Test the production logistics and quality of 136Xe; • 2000kg of natural Xe are already available by our collaborators at ITEP; • Already a respectable (20x)  decay experiment (no Ba-ion tagging at this stage);

  22. Detector • ~60 liters enriched liquid 136Xe, • In low background teflon vessel • Surrounded and shielded by ~50 cm radially low background thermal transfer fluid • Contained in a low background Cu double walled vacuum insulated cryostat • Shielded by ~ 5 cm very low background Pb • Further shielded by ~20 cm low background Pb • Located ~800 m below ground in NaCl deposit – WIPP in Carlsbad, New Mexico. • Detector is a liquid TPC with photo-detectors to provide start time and improve energy resolution of the β’s.

  23. Detector APD plane below crossed wire array 2D Detector schematic

  24. Cryostat Cross Section Refrigerant feedthroughs Heat Transfer Fluid In/Out Xenon Chamber Support Outer Door Condenser FC-87 Inner Door Xenon Heater should be on this area Xenon Chamber FC-87 1” thick Thermal Insulation (MLI-vacuum), not shown to scale Inner Copper Vessel Outer Copper Vessel

  25. Detector Full View

  26. Simplified xenon handling system diagram

  27. An experimental facility for EXO WIPP : Waste Isolation Pilot Plant Carlsbad NM

  28. Status • Enriched Xe in hand. • Clean rooms in commercial production. • WIPP agreement, including Environmental Impact, • complete. • Swiss collaborators building cryostat. • Xe purification and refrigeration issues through • R&D, purchasing of components. • Detector vessel, readout, and electronics being • engineered. • EXO could be in WIPP by Summer 2005, if • technically limited.

  29. CONCLUSIONS EXO 200kg prototype mass sensitivity • Assumptions: • 200kg of Xe enriched to 80% in 136 • σ(E)/E = 1.6% 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)

  30. 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

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