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UCNA Experiment at LANSCE

UCNA Experiment at LANSCE. First experiment to measure neutron decay correlation ( A ) with UCN UCN experiments have different systematics compared to cold neutron beams Polarization process and background sources differ significantly UCNA has no physics data yet

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UCNA Experiment at LANSCE

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  1. UCNA Experiment at LANSCE • First experiment to measure neutron decay correlation (A) with UCN • UCN experiments have different systematics compared to cold neutron beams • Polarization process and background sources differ significantly • UCNA has no physics data yet • Lots of pictures of hardware and performance!

  2. UCNA Collaboration California Institute of Technology R. Carr, B. Filippone, K. Hickerson, J. Liu, J. Martin, M. Mendenhall, B. Plaster, R. Schmid, B. Tipton, J. Yuan Institute Lau-Langevin P. Geltenbort Los Alamos National Laboratory J. Anaya, T. J. Bowles, T. Brun, M. Fowler, R. Hill, G. Hogan, T. Ito, K. Kirch, S. Lamoreaux, C.-Y. Liu, C. L. Morris, M. Makela, A. Pichlmaier, A. Saunders (co-spokesperson), S. Seestrom, P. Walstrom, J. Wilhelmy North Carolina State University/TUNL H. O. Back, L. Broussard, A. T. Holley, R. K. Jain, R. W. Pattie, K. Sabourov, A. R. Young (co-spokesperson), Y.-P. Xu Petersburg Nuclear Physics Institute A. Aldushenkov, A. Kharitonov, I. Krasnoshekova, M. Lasakov, A. P. Serebrov, A. Vasiliev Tohoku University S. Kitagaki University of Kyoto M. Hino, T. Kawai, M. Utsuro University of Washington A. Garcia, S. Hoedl, D. Melconian, A. Sallaska, S. Sjue Virginia Polytechnic Institute and State University R. Mammei, M. Pitt, R. B. Vogelaar

  3. The Caltech UCN group Nick Hutzler Gary Cheng Jenny Hsiao Riccardo Schmid Kevin Hickerson Junhua Yuan Brad Plaster Bob Carr Michael Mendenhall Jianglai Liu BF

  4. Why UCNA? • For accurate measurement of A (and Vud via neutron decay) need to characterize and minimize systematic uncertainties • Different experimental approaches are critical to reducing systematic uncertainties • PERKEO II/III UCNA Supermirror polarizer SC magnet polarizer Cold neutron beam from UCN from pulsed proton CW reactor beam Scintillator b dectector Scintillator & MWPC b detector

  5. Overview of UCNA experiment • SD2 Superthermal UCN source • See talk by M. Makela • Diamond-coated UCN guides • Polarizer and spin-flipper system • Spectrometer & b-decay detectors

  6. Experiment Design

  7. UCNA Experiment Layout Neutron Polarizing Magnets UCN Source Superconducting Spectrometer Electron Detectors

  8. UCNA experiment Experiment commissioning underway Initial goal is 0.2% measurement of A-correlation (previous measurements ~ 1% uncertainty) UCNA Liquid N2 Be reflector LHe Solid D2 77 K poly Tungsten Target

  9. Diamond-like Carbon (DLC) Coatings • Developed at Virginia Tech • High critical velocity and low depolarization. Excimer laser deposition

  10. Can coat 1 meter long quartz tubes • Can also coat UCN source parts • Available e-- beam to allow coating with Cu and Ni

  11. DLC coated Quartz Coatings analyzed with AFM, optical ellipsometry and neutron reflectometry

  12. Testing Guides with UCN @ ILL • Measurements Characterized: • Depolarization per bounce on DLC-coated guides • < 3 x 10-6 • Loss per bounce on DLC-coated guides • < 2 x 10-4

  13. UCN Polarization via high B-field “Low field seekers” “High field seekers”

  14. UCNA polarization • Pre-polarizing 6T magnet allows good UCN transport through vacuum window (isolates source and detector system for safety • 2nd 7T magnet further filters UCN and allows for spin flip • Adiabatic Fast Passage (AFP) resonator

  15. e- Polarizer/AFP Flipper

  16. AFP resonator

  17. AFP UCN in Sample during bottle emptying: change state of AFP at end of run cycle and monitor depolarized UCN leaking back to detector Depolarization Measurements UCN detector 7T Polarizer/AFP 7T UCN in Crossed polarizer: Uses AFP to flip UCN to low field seekers

  18. Recent Pictures of LANSCE Area B

  19. Recent Pictures of LANSCE Area B

  20. Neutron Decay Tube Decay Electron Detectors Superconducting Spectrometer 1 Tesla Central Field with 0.6 T field expansion to suppress backscattering

  21. UCN Decay Tube • 10 cm diameter x 300 cm long • Diamond-coated with diffusive ends

  22. Measured Spectrometer B-Field vs z-position 1.0053 x = + 4cm off-axis 1.0052 1.0051 x = 0 cm 1.0050 B-field (T) 1.0049 1.0048 x = - 4cm off-axis 1.0047 1.0046 -2.5 -2.0 -1.5 -1.0 -0.5 0 1.0 1.5 2.0 2.5 z-position (m) Measured uniformity over neutron decay volume = +/- 3.5 x 10-4 Proposal specification = +/- 5.0 x 10-4

  23. b-detectorSystem • Requirements: • Low Background, Reasonable Energy Resolution, Minimal e- Backscattering • Design: 6 mm Exit Window 6 mm Entrance Window e- 3.5 mm Scintillator Low Pressure MWPC

  24. Full Detector Schematic PMT e- PMT Fe Magnetic Shields (also vacuum seal) MWPC Preamp Cards 100 torr Neopentane 100 torr N2

  25. Assembled Detector PMT PMT

  26. Scintillator (KEK/Sizuno) 12 UVT adiabatic light guides coupled to 4 RCA8850 PMT’s

  27. MWPC Detector Thin Window 6mm Al-Mylar with Kevlar yarn Includes Cathode and Anode wire planes (x & y position)

  28. Detector Studies • At Caltech with 135 keV electron gun • At LANSCE with 113Sn source (Eb ~ 370 keV) • At LANSCE with neutron b-decay

  29. Caltech Electron Accelerator Kellogg Lab basement: E = 20 – 130 keV Can produce 1Hz – 10 THz

  30. Detailed Backscattering studies completed at Caltech (comparison with GEANT4 and PENELOPE Monte Carlo) "New measurements and quantitative analysis of electron backscattering in the energy range of neutron beta-decay", J.W. Martin et al., Phys. Rev. C. 73, 015501 (2006). "Measurement of electron backscattering in the energy range of neutron beta decay", J.W. Martin et al., Phys. Rev. C 68, 055503 (2003).

  31. Scintillator Energy Response Counts Sum of 4 PMTs Ebeam = 130 keV Energy resolution = 15% Photo-electron (pe) yield = 340 p.e./MeV

  32. Pulse Height Spectrum (Scintillator & MWPC Anode) Scintillator 120 keV e- beam MWPC

  33. Anode wire spacing Anode wire spacing MC e- Data e- MWPC reconstructed position for 120 keV e- at normal incidence Monte Carlo B = 1 T y z x Cathode wires Data Anode wires

  34. Spectrometer studies at LANSCE with 113Sn source in 1T field Fiducial Volume Cut

  35. Cosmic ray induced events

  36. Neutron b-decay measurements in in Spectrometer Fiducial Volume Radius 28Al b-decay - via 27Al(n,g) Decay Tube Radius 28Al: 2.2 min., Eb = 2.9 MeV endpoint

  37. Scintillator rate increases during beam pulses Room Background

  38. First UCNA Spectrum 11/06

  39. Signal vs Background in UCN b-decay Total background rate < 0.15 Hz

  40. UCNA Status • All major systems commissioned • First measured b-decay: 11/06 with 2 Hz • Upgrades to UCN source expected to provide > factor 3 increase in b-decay rate for 2007 • Goal for 07 run: few % measurement of A with UCN for first time • Further upgrades to source (better UCN Guides, increased beam current) should give additional factor of 3-4 • Goal for 08-09: < 0.5% measurement, dominated by statitistics

  41. Additional Slides

  42. Sources of depolarization • Material depolarization – already benchmarked at ILL less than 2x10-6 per bounce • Majorana transitions – Monte Carlo treatment exists: less than 2x10-4 per pass (holding fields  40G) • Wall collisions in gradient fields – Monte Carlo treatment exists less than 1x10-4 per pass in field reversal region and AFP region • AFP performance – Monte Carlo exists, benchmark exists less than 1x10-4 per pass (from Monte Carlo), benchmarked at ILL 99.7±.3% efficient • “Fast” UCN –Monte Carlo treatment exists less than 1x10-3 from MC

  43. Measuring Depolarization “polarimetry” = measuring depolarized UCN(when depolarization is small, only modest accuracy is required) • Crossed polarizers – low transport model dependence allows for monitoring of depolarization and spin-flip efficiency • Monitoring during bottle decay time – minimal additional equipment, polarization and spin-flip information after each run cycle • Additional information from time dependence of asymmetry • With proton detection, B coefficient (A=1) is in situ monitor of polarization. Current knowledge of B gives polarimetery to 0.4%. Alternatively provides polarization independent result for gA/gV and least model dependence.

  44. Statitistics of UCNA • A sensitivity: • sA/A ~ 3%/month/sqrt(Hz)

  45. Solenoid Bore Tube • 35 cm diameter SS tube • Coated with 6LiF-loaded TPX • TPX reduces UCN potential to allow capture • UCN Monitors placed at decay tube exit UCN Monitors (6LiF-coated Si) 6LiF/TPX coated bore tube MWPC MWPC Decay Tube 6LiF/TPX UCN baffles

  46. Spectrometer Polarizer AFP magnet Pre-polarizer magnet LHe plant UCN Source Experiment Layout Proton Beam

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