1. EXO-Development Program DUSEL Workshop Washington, November 2007 David Sinclair Carleton/TRIUMF

2. We need to develop new strategies to eliminate backgrounds to probe the allowed space Barium tagging may offer a way forward Inverted Normal

3. Xe offers a qualitatively new tool against background: 136 Xe 136 Ba ++ 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 10 7 /s Important additionalImportant additional constraint constraint Huge backgroundHuge background reduction reduction 2 P 1/2 4 D 3/2 2 S 1/2 493nm 650nm metastable 80s 136 Ba+

4. Ba + spectroscopy in high pressure noble gases RF quadrupole trap loaded in UHV from a Ba dispenser and e-beam ionizer Xe can be injected while observing the ions

5. Millikan experiment with ions in vacuum Start with a ● Start with a large signal large signal ● Use the endcap bias voltage to bias voltage to make the trap make the trap unstable and unstable and drop ions drop ions ● Keep unloading till trap is empty trap is empty Start End

6. The signal amplitude is proportional to integers Millikan experiment with ions in vacuum

7. 1) Resonance Ionization Spectroscopy After a real-time ββ trigger, a ~400 μm fiber with a metallized end and biased at a negative potential is inserted near the event site in LXe. The Ba + ion is attracted to the tip and trapped The ion is released with a laser pulse, resonantly ionized with two other pulses, and injected into the trap where it is detected. Ba tagging for the Liquid Detector Currently, two ion transfer methods are under parallel development, both involving the capture and transport of the ion on the surface of a specially designed tip

8. Cryo-tip sensor Cu cold finger Au-coated leads Vespel sleeves W heater wire lHe cryostat Ice sensor LXe cell Actuator Shielded cables To LCR meter 2mm Read-out cables

9. Results – PID-controlled Thin Layer Freezing in 700 mbar Xe from liquid Xe PID control temp, feedback on capacitance

10. Liquid or Gas Liquid Compact detector No pressure vessel Small shield -> lower purity reqd. Gas Energy resolution Tracking & multi-site rejection In-situ Ba tagging  angular correlation Large Cryostat Poorer energy, tracking resolution Ex-situ Ba tagging Large detector Needs very large shield Pressure vessel is massive Pros Cons

11. Understanding Physics of Double Beta Decay Recent paper by Ali, Borisov and Zhuridov Probing New Physics in the Neutrinoless Double Beta Decay using Electron Aangular Correlation arXiv:0706.4165v2

12. Anode Pads Micro-megas WLS Bar Electrode For 200 kg, 10 bar, box is 1.5 m on a side Possible concept for a gas double beta counter Xe Gas + ???.... PMT Laser Grids

13. Technical issues for a Gas counter Need to demonstrate good energy resolution (<1% to completely exclude  ) Want to have gas gain if possible Need to demonstrate Ba tagging  Deal with pressure broadening  Ba ion lifetime  Ba++ -> Ba+ conversion  Can we cope with background of scattered light

14. Progress on energy resolution Alpha spectrum at 2 b pressure.  = 0.6%

15. Energy Resolution in Gas Better than 1% (sigma) achieved in pure Xe and several mixtures In pure Xe, at 2 bar, amplitude is constant to 0.2% for drift up to 17 cm Pure Xe is slow

16. Other gas requirements If we add something to the gas to speed up electrons and quench gain stage then  Does the additive kill the 172 nm light  Do electrons attach to the additive  Will the additive trap Ba ions  Will the additive convert Ba++ to Ba+

17. Ba tagging in high-pressure Xe We need to deal with pressure broadening Requires higher laser power to get fluorescence rate (perhaps factor of 1000) Higher density gives more scattering However, in high pressure Xe the D state will quickly de-excite collisionally Plan to excite with blue laser and look for red emission photons

18. Xe offers a qualitatively new tool against background: 136 Xe 136 Ba ++ 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 10 7 /s Important additionalImportant additional constraint constraint Huge backgroundHuge background reduction reduction 2 P 1/2 4 D 3/2 2 S 1/2 493nm 650nm Laser In Red light out De-excite by collisions

19. Future Program Demonstrate the liquid detection technique at WIPP, measure (  in Xe, Measure (  if at HM value Develop the Ba tagging for a liquid detector Demonstrate a gas phase detection Develop the Ba in-situ tag in gas phase Build the ultimate, ton scale detector for double beta decay