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 Observatory for double beta decay

Double Beta Decay - - d(n) u(p) e c e e W W d(n)u(p) c e e - c eReR W d(n) u(p) W e - eLeL

To improve on T 12 0 and : need large source mass lower background, better event signature

E ee dN dt    E0E0 (A,Z) 0+ (A,Z+1) (A,Z+2) E0E0 e-e-e-e- Popular candidates E 0 (MeV)Abundance (%) Ca 76 Ge Se 82 Kr Mo 100 Ru Te 128 Xe Te 130 Xe Xe 136 Ba Nd 150 Sm Th 232 U 238 U 238 Pu dir dir, geo dir dir, geo dir melking dir

Isotopic enrichment for a gaseous substance like Xe is most economically achieved by ultracentrifugation This separation step that rejects the light fraction is also very effective in removing 85 Kr (T 1/2 =10.7 yr) that is present in the atmosphere from spent fuel reprocessing Russia has enough production capacity to process 100 ton Xe and extract up to 10 ton 136 Xe in a finite time

NucleusQRPA Caltech Shell model Strasbourg- Madrid exp 48 Ca x Ge x Se x Mo x Te x Te X Te x Xe<1.0<2.6>8.1 x direct geochem. 

Enriched Xenon Observatory for double beta decay Alabama, Caltech, Carleton, Colorado, UC Irvine, ITEP Moscow, Laurentian, Neuchatel, SLAC, Stanford Ba+ system best studied (Neuhauser, Hohenstatt, Toshek, Dehmelt 1980) Very specific signature “shelving” Single ions can be detected from a photon rate of 10 7 /s 2 P 1/2 4 D 3/2 2 S 1/2 493nm 650nm metastable 47s Much improved signature! 136 Xe: 136 Ba++ e- e- final state can be tagged using optical spectroscopy (M.Moe PRC44 (1991) 931) optical spectroscopy (M.Moe PRC44 (1991) 931)

Two detector options under consideration High Pressure gas TPC High Pressure gas TPC 5-10 atm, 50 m 3 modules, 5-10 atm, 50 m 3 modules, 10 modules for 10 t 10 modules for 10 t Xe enclosed in a non-structural bagXe enclosed in a non-structural bag  range ~5-10cm:  range ~5-10cm: can resolve 2 blobs can resolve 2 blobs 2.5m e-drift at ~250kV2.5m e-drift at ~250kV Readout Xe scintillation withReadout Xe scintillation with WLSB (T0) WLSB (T0) Additive gas: quenching andAdditive gas: quenching and Ba ++ Ba + neutralization Ba ++ Ba + neutralization Steer lasers or drift Ba-ion toSteer lasers or drift Ba-ion to detection region detection region Liquid Xe chamber Liquid Xe chamber Very small detector (3m 3 for 10tons)Very small detector (3m 3 for 10tons) Need good E resolutionNeed good E resolution Position info but blobs not resolvedPosition info but blobs not resolved Readout Xe scintillationReadout Xe scintillation Can extract Ba from hi-density XeCan extract Ba from hi-density Xe Spectroscopy at low pressure:Spectroscopy at low pressure: 136 Ba (7.8% nat’l) different 136 Ba (7.8% nat’l) different signature from natural Ba signature from natural Ba (71.7% 138 Ba) (71.7% 138 Ba) No quencher needed, neutralizationNo quencher needed, neutralization done outside the Xe done outside the Xe

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

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

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

Have demonstrated that we can get sufficient energy resolution in LXe to separate the 2 ν from the 0 ν modes We can do ionization measurements as well as anyone Now we turn on our new correlation technique… Resolutions at 570 keV or

Fishing ions in LXe

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

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

CCD Image of Ba + ions in the trap Trap edge

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

In parallel, build liquid TPC prototype, without Ba tagging Prototype Scale: –200 Kg enriched 136 Xe –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 2 mode –Set decent limit for 0 mode (probe Heidelberg- Moscow)

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

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

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

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

Full detector view With Pb shielding

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

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.

200 kg prototype, estimated sensitivity, without Ba tagging Estimate background from radioactivity (2  negligible) Mass (kg) Enrichment (%) Eff. (%)  MeV (%) Time (yr) Background (events) T 1/2 0 (yr) (eV) RQRPA * V. A. Rodin et al. Phys.Rev. C68 (2003)

Ultimate sensitivity, assuming 1) that the Xe chamber + Ba tagging gives 0 background from radioactivity... 2) that the energy resolution is  (E)/E=2 % (2  background!) Conclusion: With a coordinated effort, the meV region is within reach! Mass (kg) Enrichment (%) Eff. (%)  MeV (%) Time (yr) Background (events) T 1/2 0 (yr) (eV) RQRPA (use 1) 0.7 (use 1) 2.0* *