Z.Djurcic, D.Leonard, A.Piepke Physics Dept, University of Alabama, Tuscaloosa AL P.Vogel

1. 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, 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

2. c  e c  e - e c  eR  eL - e Double Beta Decay d(n) u(p) - e W W - e u(p) d(n) d(n) u(p) W W u(p) d(n)

3. To improve on T120n and <mn>: need large source mass lower background, better event signature

4. dN dt 2n c0 0n (A,Z+1) 0+ 2+ (A,Z) E0 0+ e-e- (A,Z+2) Eee E0 E0 (MeV) Abundance (%) 48Ca 48Ca 4.271 0.187 dir 76Ge 76Ge 2.040 7.8 dir Popular candidates 82Se 82Kr 2.995 9.2 dir, geo 100Mo 100Ru 3.034 9.6 dir 0.868 128Te 128Xe 31.4 dir, geo 130Te 130Xe 2.533 34.5 dir, geo 136Xe 136Ba 2.479 8.9 dir 150Nd 150Sm 3.367 5.6 dir 232Th 232U 0.858 100 238U 238Pu 1.145 99.3 melking

5. Isotopic enrichment for a gaseous substance like Xe is most economically achieved by ultracentrifugation Russia has enough production capacity to process 100 ton Xe and extract up to 10 ton 136Xe in a finite time This separation step that rejects the light fraction is also very effective in removing 85Kr (T1/2=10.7 yr) that is present in the atmosphere from spent fuel reprocessing

6. bb2n direct geochem. direct

7. Enriched Xenon Observatoryfor double beta decay 2P1/2 650nm 493nm metastable 47s 4D3/2 2S1/2 Alabama, Caltech, Carleton, Colorado, UC Irvine, ITEP Moscow, Laurentian, Neuchatel, SLAC, Stanford 136Xe: 136Ba++ e- e- final state can be tagged using optical spectroscopy (M.Moe PRC44 (1991) 931) Much improved signature! 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

8. Two detector options under consideration • High Pressure gas TPC • 5-10 atm, 50 m3 modules, • 10 modules for 10 t • Xe enclosed in a non-structural bag • b range ~5-10cm: • can resolve 2 blobs • 2.5m e-drift at ~250kV • Readout Xe scintillation with • WLSB (T0) • Additive gas: quenching and • Ba++ Ba+ neutralization • Steer lasers or drift Ba-ion to • detection region • Liquid Xe chamber • Very small detector (3m3 for 10tons) • Need good E resolution • Position info but blobs not resolved • Readout Xe scintillation • Can extract Ba from hi-density Xe • Spectroscopy at low pressure: • 136Ba (7.8% nat’l) different • signature from natural Ba • (71.7% 138Ba) • No quencher needed, neutralization • done outside the Xe

10. s(E)/E=0.13 % at 2.48 MeV ! Energy resolution F=0.19, W=22 eV Gotthard 5 bar xenon a (from cathode), 210Po (238U chain) quenching (a/e-)=1/6.5 s(E)/E=1.1 % at 2.48 MeV ! e-, 232Th s(E)/E=3.4 % at 1.59 MeV s(E)/E= 2.7 % at 2.48 MeV

11. ITEP-Moscow, Kharkov, Neuchâtel Light detection (electroluminescence)in xenon (+CF4?) e- track Grid (metallic cloth) Multianode photomultiplier UV photons Anode (charge) Two gap scheme: Grid (metallic cloth) Optical fibers x-y Doped fibers : 1 step WLS UV (180 +/-20nm) to blue or 2 step WLS with coated fibers anode Fibers (250 mm)

12. Found a clear (anti)correlation between ionization and scintillation 1 kV/cm ~570 keV Major effort now: liquid xenon

13. Have demonstrated that we can get sufficient energy resolution in LXe to separate the 2νfrom the 0νmodes We can do ionization measurements as well as anyone Resolutions at 570 keV Now we turn on our new correlation technique… 3.3%@570keV or 1.6%@2.5MeV

14. Fishing ions in LXe

15. 230U source α spectrum as delivered by LLNL and measured in vacuum 230U (20.8d) α 5.99MeV 226Th (30.5min) α 6.45MeV 222Ra (38s) α 6.68MeV 218Rn (35ms) α 7.26MeV 214Po (164ms) α 7.83MeV αspectrum from whatever is grabbed by the tip (in Xe atmosphere) 210Pb (22yr) Initial Ra/Th ion grabbing successful As expected release from a finite size metallic tip is challenging

16. Ion Trap R&D at UHV/atmospheric pressure RF quadrupole trap loaded in UHV from a Ba dispenser and e-beam ionizer Xe can be injected while observing the ions

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

18. Indeed we are talking about single ions: one can load the trap with multiple ions and then observe the signal intensity as ions are dropped one by one… Zero ion background All above in UHV; Perform the same experiment in noble gas atmosphere

19. In parallel, build liquid TPC prototype, without Ba tagging • Prototype Scale: • 200 Kg enriched 136Xe • All functionality of EXO except Ba identification • Operate in WIPP for ~two years • Prototype Goals: • Test all technical aspects of EXO (except Ba id) • Measure 2n mode • Set decent limit for 0n mode (probe Heidelberg-Moscow)

20. Massive materials qualification program led by Alabama with contributions from Carleton, Laurentian and Neuchatel • Approximate detector simulation with material properties to • establish target activities • NAA whenever possible (MIT reactor + Alabama) • Direct Ge counting at Neuchatel, Alabama and soon Canada • High sensitivity mass spectroscopy starting in Canada • Alpha counting at Carleton and Stanford • Rn outgassing measurements starter at Laurentian (Xe plumbing) • Full detector simulation in progress

21. Detector Teflon vessel (356 on each side, 16 mm diameter 120 % QE in UV))

22. APD plane below crossed wire array 100 APD channels (7 APD grouped together) provide light and t0 200 ionization channels (groups of wires 100 x +100 y) Can define fiducial volume

23. Cryostat Cross Section Outer Door Condenser FC-87 Xenon Chamber Inner Door Xenon Chamber Support Xenon Heater should be on this area FC-87 1” thick Thermal Insulation (MLI-vacuum), not shown to scale Inner Copper Vessel Outer Copper Vessel

24. Full detector view With Pb shielding

25. DoE’s Waste Isolation Pilot Plant (WIPP), Carlsbad NM

27. Status • Enriched Xe in hand. • Clean room installed at Stanford. • WIPP agreement, including Environmental Impact, complete. • Cryostat being designed. • Xe purification and refrigeration issues being finalized • Detector vessel, readout, and electronics being engineered.

28. 200 kg prototype, estimated sensitivity, without Ba tagging Estimate background from radioactivity (2nbb negligible) V. A. Rodin et al. Phys.Rev. C68 (2003) 044302

29. Ultimate sensitivity, assuming 1) that the Xe chamber + Ba tagging gives 0 background from radioactivity... 2) that the energy resolution is s(E)/E=2 % (2nbb background!) Conclusion: With a coordinated effort, the meV region is within reach!