html5-img
1 / 66

EXO Gas

EXO Gas. Progress and Plans October, 2008 David Sinclair. EXO Collaboration. Canada Carleton, Laurentian USA Alabama, Caltech, Colorado State, UC irvine, Maryland, Massachusetts, SLAC, Stanford Switzerland Bern Russia ITEP. EXO People. Canadian Team . Laurentian

warren-hines
Télécharger la présentation

EXO Gas

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. EXO Gas Progress and Plans October, 2008 David Sinclair

  2. EXO Collaboration • Canada • Carleton, Laurentian • USA • Alabama, Caltech, Colorado State, UC irvine, • Maryland, Massachusetts, SLAC, Stanford • Switzerland • Bern • Russia • ITEP

  3. EXO People

  4. Canadian Team • Laurentian • Jacques Farine, Doug Hallman, Ubi Wichoski • Carleton • Madhu Dixit, Kevin Graham, Cliff Hargrove, David Sinclair • Christina Hagemann (RA Arrives 2 weeks) • Etienne Rollin (PhD Student) • Chad Greene, James Lacey (MSc students) • Currently 3 undergraduate thesis/project students

  5. New effort for the gas phase • NSF grants to Stanford and Alabama for RA,s students to work on gas EXO • New EXO collaborators at ITEP who have just completed a Xe TPC project • Possible collaboration with Spanish group

  6. Heidelberg-Moscow Results for Ge double beta decay 57 kg years of 76Ge data Apply single site criterion

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

  8. EXO – Enriched Xenon Observatory • Look for neutrino-less double beta decay in Xe • 136Xe --- 136Ba + e- + e- • Attempt to detect ionization and the Ba daughter • Ba is produced as ++ ion • Ba+ has 1 electron outside Xe closed shell so has simple ‘hydrogenic’ states • Ba++ can (?) be converted to Ba+ with suitable additive

  9. Advantages of Xe • Like most noble gases/liquids it can be made extremely pure • No long lived radioactive isotopes • High Q value gives favourable rates • Readily made into a detector • Possible barium tagging to eliminate backgrounds

  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 Large detector Needs very large shield Pressure vessel is massive Large Cryostat Poorer energy, tracking resolution Ex-situ Ba tagging

  11. EXO 200 • A 200 kg liquid xenon detector is nearing completion at WIPP • We play a major role in this project and there is on-going activity at SNOLAB supporting this project • This talk will focus on the gas counter as this is a potential candidate for a SNOLAB project

  12. Xe offers a qualitatively new tool against background: 136Xe 136Ba++ 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 107/s 2P1/2 650nm 493nm 4D3/2 • Important additional • constraint • Huge background • reduction metastable 80s 2S1/2

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

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

  15. Program as stated last year • Need to demonstrate good energy resolution (<1% to completely exclude bb2n ) tracking, • Need to demonstrate Ba tagging • Deal with pressure broadening • Ba ion lifetime • Ba++ -> Ba+ conversion • Can we cope with background of scattered light

  16. Tasks to design gas EXO • 1) Gas Choice • Measure Energy resolution for chosen gas • (Should be almost as good as Ge but this has never been achieved) • Measure gain for chosen gas • Measure electron attachment for chosen gas • Understand optical properties • Measure Ba++ -> Ba+ conversion • Measure Ba+ lifetime

  17. Tasks to design EXO Gas • 2) TPC Design • What pressure to use • What anode geometry to use • What chamber geometry to use • What gain mechanism to use • Develop MC for the detector • Design electronics/DAQ

  18. Tasks to design EXO Gas • 3) Ba Tagging • Demonstrate single ion counting • Understand pressure broadening/shift • Understand backgrounds • Fix concept

  19. Tasks to design EXO Gas • 4) Overall Detector concept • Fix shielding requirements and concepts • Design pressure containment • Fix overall layout

  20. Gas Properties • Possible gas – Xe + iso-butane + TEA • Iso-butane to keep electrons cold, stabilize micromegas/GEM • TEA • Converts Ba++ -> Ba+ • Q for TEA + Ba++->TEA+ + Ba+* ~ 0 • Converts 172 nm -> 280 nm? • ? Does it trap electrons? • ?Does it trap Ba+?

  21. Progress This Year

  22. Movable source holder Contacts rings with wiper Field Rings Source Grid Anode Gridded Ion Chamber

  23. Progress on energy resolution – Pure Xe, 2 Bar s = 0.6% Alpha spectrum at 2 b pressure.

  24. Program with Gridded Ion Chamber • Response for many gas mixtures measured • New data on drift velocities in Xe + Methane, isobutane, TEA • Some electron attachment measured but may be due to gas impurities

  25. First efforts with Micromegas • Grid and anode of chamber replaced by micromegas • Collaboration with Saclay and CERN to produce micromegas • Using new ‘microbulk’ form of micromegas as this is thought to offer best resolution • Ion density with alphas too high for this technology – resolution ~ 1.7% • Switch to betas

  26. Spectroscopy with micromegas 22 keV 109Cd source

  27. Status of Micromegas • Energy resolution of 4% observed for 22 keV x-ray is promising (-> 0.4% at 2 MeV) • Microbulk technology is not sufficiently robust for this application • Xe requires high fields for gas gain and lifetime of the micromegas is hours for these fields • Will attempt again with the T2K style micromegas

  28. Progress on Detector Simulations • Double beta events being simulated in Xe gas using GEANT and EGS • Tracks are ugly!

  29. Containment of tracks

  30. Case for mixed gas • There is incentive from previous slides to investigate a mixed gas (Ne-Xe or He-Xe) • Tracks in the lighter are straighter • Better containment for given amount of (expensive) xenon

  31. Ratio of projected track to the total track length

  32. Measuring the scintillation light signal

  33. Energy and position response for scintillation light

  34. Light from gas mixtures • (this slide intentionally left blank)

  35. Measuring scintillation light in Xe gas mixtures • It appears that any quench gas in Xe kills the scintillation light • It appears that the mechanism is not absorption of the photons but interaction between Xe dimers and the additives which de-excite the dimers.

  36. Barium tagging Original concept Pulse 493 nm laser to Excite D state Then pulse 650 nm Laser to un-shelf D state 2P1/2 650nm 493nm 4D3/2 metastable 80s Does not work! 2S1/2

  37. New Concept for Laser Tagging in High Pressure • The D state is quenched by gas interactions in ns • So – use only blue laser, look for red light

  38. Barium fluorescence Observed

  39. Status of tagging • A number of linewidth measurements made with the arc source • Changing from an arc source to a laser ablation source • We have demonstrated production of about 105 ions/pulse using an old N2 laser • We are about to modify chamber to introduce this source

  40. New Detector Concept • We have some as yet unresolved issues with the original concept • We do not get scintillation light with quenchers but we cannot have gas gain without • We are concerned that additives such as TEA will give us gas purification difficulties so how do we convert Ba++ to Ba+ and we do not know that TEA like additives will not form molecules or clusters with the Ba ions

  41. New Concept • Identify the barium production by extracting the ion into vacuum and using conventional techniques to identify a mass 136, ++ ion. • Expect this to be unique to Ba • Operate the detector in pure noble gas (Xe or Xe+Ne) • Use electroluminescence in place of gas electron gain

  42. Concept for an electroluminescence readout Design copied from Fermilab RICH counter

  43. Electroluminescence Demonstration • EL is a well studied technique in noble gases and mixed noble gases • EL is preferred over electron proportional counters for gamma ray detectors • In Ne + Xe all of the light comes out at the Xe scintillation wavelength (175 nm) for admixtures of >1% Xe • No-one has demonstrated energy resolution in MeV range • We propose to construct a detector to establish performance of EL for this application

  44. We plan a 20 x 20 array of 2 cm pads on each end

  45. Barium Identification • Because of the complexity of the electron tracks in Ba, it will be hard to determine exactly where the Ba is produced. • We have some volume within which it will be contained. • Transport that ‘volume’ to the edge of the detector • Stretch and squeeze it using field gradient into a long pipe

  46. Barium Identification (Cont) • At end of pipe have an orifice leading to evacuated region • Trap ions as they leave the gas using a Sextupole Ion Trap (SPIG) • Once the ion is in vacuum, use conventional techniques to identify it (eg Wein filter + quadrupole MS or TOF + rigidity or ….

  47. Critical Design Point • What is the efficiency for getting the ion out of the pipe and trapped by the spig? • We will start by simulations for the trap varying trap geometry, pressures, gas mix • Possibly do tests on existing traps • Look at improving delivery of ions down pipe using RF carpets or FAIMS

  48. RF Carpets RF Funnels

More Related