UCNA Experiment at LANSCE First experiment to measure

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!

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 (cospokesperson), 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

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

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 Supermirror polarizer Cold neutron beam from CW reactor Scintillator b dectector UCNA SC magnet polarizer UCN from pulsed proton beam Scintillator & MWPC b detector

Overview of UCNA experiment • SD 2 Superthermal UCN source – See talk by M. Makela • Diamond-coated UCN guides • Polarizer and spin-flipper system • Spectrometer & b-decay detectors

Experiment Design

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

UCNA experiment Experiment commissioning underway Initial goal is 0. 2% measurement of A-correlation (previous measurements ~ 1% uncertainty) Liquid N 2 Be reflector LHe Solid D 2 77 K poly Tungsten Target UCNA

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

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

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

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

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

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

Polarizer/AFP Flipper e-

AFP resonator

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

Recent Pictures of LANSCE Area B

Recent Pictures of LANSCE Area B

Superconducting Spectrometer 1 Tesla Central Field with 0. 6 T field expansion to suppress backscattering Neutron Decay Tube Decay Electron Detectors

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

Measured Spectrometer B-Field vs z-position 1. 0053 x = + 4 cm off-axis B-field (T) 1. 0052 1. 0051 1. 0050 x = 0 cm 1. 0049 1. 0048 x = - 4 cm off-axis 1. 0047 1. 0046 -2. 5 -2. 0 -1. 5 -1. 0 -0. 5 0 z-position (m) 1. 0 Measured uniformity over neutron decay volume = +/- 3. 5 x 10 -4 Proposal specification = +/- 5. 0 x 10 -4 1. 5 2. 0 2. 5

b-detector System • 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

Full Detector Schematic PMT e- PMT Fe Magnetic Shields (also vacuum seal) 100 torr N 2 MWPC Preamp Cards 100 torr Neopentane

Assembled Detector PMT

Scintillator (KEK/Sizuno) 12 UVT adiabatic light guides coupled to 4 RCA 8850 PMT’s

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

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

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

Detailed Backscattering studies completed at Caltech (comparison with GEANT 4 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).

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

Pulse Height Spectrum (Scintillator & MWPC Anode) Scintillator 120 ke. V e- beam MWPC

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

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

Cosmic ray induced events

Neutron b-decay measurements in in Spectrometer Fiducial Volume Radius 28 Al Decay Tube Radius 28 Al: b-decay - via 27 Al(n, g) 2. 2 min. , Eb = 2. 9 Me. V endpoint

Scintillator rate increases during beam pulses Room Background

First UCNA Spectrum 11/06

Signal vs Background in UCN b-decay Total background rate < 0. 15 Hz

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

Additional Slides

Sources of depolarization • Material depolarization – already benchmarked at ILL less than 2 x 10 -6 per bounce • Majorana transitions – Monte Carlo treatment exists: less than 2 x 10 -4 per pass (holding fields 40 G) • Wall collisions in gradient fields – Monte Carlo treatment exists less than 1 x 10 -4 per pass in field reversal region and AFP region • AFP performance – Monte Carlo exists, benchmark exists • “Fast” UCN less than 1 x 10 -4 per pass (from Monte Carlo), benchmarked at ILL 99. 7±. 3% efficient – Monte Carlo treatment exists less than 1 x 10 -3 from MC

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 g. A/g. V and

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

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

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

CKM Summary: New tn !! UCNA 1% A measurement