Observatory for double beta decay

Transcription

1 Enriched Xenon Observatory for double beta decay 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

2 Double Beta Decay c c 1) ββ2ν: ( AZ, ) ( AZ, + 2) + e + e + ν e + ν e d(n) d(n) W W u(p) u(p) e- c νc e ( 12 / ) = ( 0, ) 2) ββ0ν : ( AZ, ) ( AZ, + 2) + e + e d(n) d(n) W m ν ν c er u(p) ν e e e - ν W el e - u(p) m ν ν ν 2ν 2 T G E Z M GT = ( ν) T 0 1/ 2 G 2N i= 1 0ν 1 = 0ν 0ν 2 ( E, Z) M VM m m U j 0 L ej U L ej GT g g 2 2 A L = 0 L = 2 F 2 ν

3 To improve on T 12 0ν and <m ν >: need large source mass lower background, better event signature

4 dn dt 2ν χ 0 0ν 0+ (A,Z+1) (A,Z) e - e E 0 (A,Z+2) E ee E 0 Popular candidates E 0 (MeV) Abundance (%) 48 Ca 48 Ca Ge 76 Ge Se 82 Kr Mo 100 Ru Te 128 Xe Te 130 Xe Xe 136 Ba Nd 150 Sm dir dir dir, geo dir dir, geo dir, geo dir dir 232 Th 232 U 238 U 238 Pu 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 136 Xe in a finite time 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

6 ββ2ν T T calc 1/ 2 exp 1/ 2 T T calc 1/ 2 exp 1/ 2 T ν 2 1/ 2 ( yr) Nucleus QRPA Caltech Shell model Strasbourg- Madrid exp 48 Ca x Ge x direct 82 Se x Mo x Te x Te X geochem. 130 Te x direct 136 Xe <1.0 <2.6 >8.1 x 10 20

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

8 Two detector options under consideration High Pressure gas TPC 5-10 atm,, 50 m 3 modules, 10 modules for 10 t Xe enclosed in a non-structural bag β range ~5-10cm: can resolve 2 blobs 2.5m e-drift e 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 (3m 3 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: 136 Ba (7.8% nat l) ) different signature from natural Ba (71.7% 138 Ba) No quencher needed, neutralization done outside the Xe

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10 Energy resolution σ ( E)/E = F(E/W)/E ββ2ν x 10 4 F=0.19, W=22 ev ββ0ν σ(e)/e=0.13 % at 2.48 MeV! Gotthard 5 bar xenon E/E 0 e -, 232 Th σ(e)/e=3.4 % at 1.59 MeV σ(e)/e= 2.7 % at 2.48 MeV α (from cathode), 210 Po ( 238 U chain) quenching (α/e - )=1/6.5 σ(e)/e=1.1 % at 2.48 MeV!

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

12 Major effort now: liquid xenon Found a clear (anti)correlation between ionization and scintillation tion 1 kv/cm ~570 kev

13 Have demonstrated that we can get sufficient energy resolution in LXe to separate the 2ν2 from the 0ν0 modes We can do ionization measurements as well as anyone Resolutions Resolutions at at kev kev Now we turn on our new correlation technique or

14 Fishing ions in LXe

15 230 U (20.8d) α 226 Th (30.5min) α 218 Rn (35ms) α α α 222 Ra (38s) 214 Po (164ms) 210 Pb (22yr) 5.99MeV 6.45MeV 6.68MeV 7.26MeV 7.83MeV Initial Ra/Th ion grabbing successful 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) 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 e 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 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 2ν mode Set decent limit for 0ν 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 Heater should be on this area FC-87 Xenon Chamber Support 1 thick Thermal Insulation (MLIvacuum), not shown to scale Outer Copper Vessel Inner Copper Vessel

24 Full detector view With Pb shielding

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

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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 (2νββ negligible) Mass (kg) Enrichment (%) Eff. (%) MeV (%) Time (yr) Background (events) T 1/2 0ν (yr) <m ν >(ev) RQRPA * V. A. Rodin et al. Phys.Rev. C68 (2003)

29 Ultimate sensitivity, assuming 1) that the Xe chamber + Ba tagging gives 0 background from radioactivity... 2) that the energy resolution is σ(e)/e=2 % (2νββ background!) Mass (kg) Enrichment (%) Eff. (%) σ/e@2.5 MeV (%) Time (yr) Background (events) T 1/2 0ν (yr) <m ν >(ev) RQRPA (use 1) 0.7 (use 1) 2.0* * Conclusion: With a coordinated effort, the mev region is within reach!