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 CollaborationCalifornia 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-LangevinP. Geltenbort
Los Alamos National LaboratoryJ. 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/TUNLH. O. Back, L. Broussard, A. T. Holley, R. K. Jain, R. W. Pattie, K. Sabourov, A. R. Young (co-
spokesperson), Y.-P. XuPetersburg Nuclear Physics Institute
A. Aldushenkov, A. Kharitonov, I. Krasnoshekova, M. Lasakov, A. P. Serebrov, A. VasilievTohoku University
S. KitagakiUniversity of Kyoto
M. Hino, T. Kawai, M. UtsuroUniversity of Washington
A. Garcia, S. Hoedl, D. Melconian, A. Sallaska, S. SjueVirginia Polytechnic Institute and State University
R. Mammei, M. Pitt, R. B. Vogelaar
The Caltech UCN group
Nick HutzlerGary ChengJenny HsiaoRiccardo SchmidKevin HickersonJunhua YuanBrad Plaster Bob CarrMichael MendenhallJianglai LiuBF
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 dectector Scintillator & MWPC detector
Overview of UCNA experiment
• SD2 Superthermal UCN source
– See talk by M. Makela
• Diamond-coated UCN guides
• Polarizer and spin-flipper system
• Spectrometer & -decay detectors
Experiment Design
UCNA Experiment Layout
Superconducting Spectrometer
Electron Detectors
Neutron Polarizing Magnets
UCN Source
Liquid N2
Be reflector
Solid D2
77 K poly
Tungsten Target
LHe
UCNA experimentExperiment commissioning underwayInitial goal is 0.2% measurement of A-correlation (previous measurements ~ 1% uncertainty)
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
Measurements Characterized:
• Depolarization per bounce on DLC-coated guides
< 3 x 10-6
• Loss per bounce on DLC-coated guides
< 2 x 10-4
Testing Guides with UCN @ ILL
UCN Polarization via high B-field
T 6B if EBV UCN
UCNE
B
n
99.9%P with neutrons polarized produce Can
n
“High field seekers”
“Low field seekers”
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
Polarizer/AFP Flipper
e-
AFP resonator
Depolarization Measurements
Crossed polarizer: Uses AFP to flip UCN to low field seekers
UCN inSample during bottle emptying: change state of AFP at end of run cycle and monitor depolarized UCN leaking back to detector
UCN in
7T
Polarizer/AFP7T
AF
P
UCN detector
Recent Pictures of LANSCE Area B
Recent Pictures of LANSCE Area B
Superconducting Spectrometer
Neutron Decay Tube
Decay Electron Detectors
1 Tesla Central Fieldwith 0.6 T field expansion to
suppress backscattering
UCN Decay Tube • 10 cm diameter x 300 cm long
• Diamond-coated with diffusive ends
Midterm
460
470
480
490
500
510
520
530
0 0.5 1 1.5 2 2.5 3 3.5 4 4.5
Gr ade
Measured Spectrometer B-Field vs z-position
z-position (m)
x = + 4cm off-axis
x = - 4cm off-axis
x = 0 cm
1.0053
1.0052
1.0051
1.0050
1.0049
1.0048
1.0047
1.0046
-2.5 -2.0 -1.5 -1.0 -0.5 0 1.0 1.5 2.0 2.5
B-f
ield
(T
)
Measured uniformity over neutron decay volume = +/- 3.5 x 10-4
Proposal specification = +/- 5.0 x 10-4
-detector System• Requirements:
– Low Background, Reasonable Energy Resolution, Minimal e- Backscattering
• Design:
6 m Entrance Window
Low Pressure MWPC
3.5 mm Scintillator e-
6 m Exit Window
Full Detector Schematic
MWPC Preamp Cards
e-PMT
PMT
Fe Magnetic Shields (also vacuum seal)
100 torr Neopentane100 torr N2
Assembled Detector
PMT
PMT
Scintillator (KEK/Sizuno)
12 UVT adiabatic light guides coupled
to 4 RCA8850 PMT’s
MWPC Detector
Thin Window6m Al-Mylar with Kevlar
yarn
Includes Cathode and Anode wire planes (x & y position)
Detector Studies
• At Caltech with 135 keV electron gun
• At LANSCE with 113Sn source (E ~ 370 keV)
• At LANSCE with neutron -decay
Caltech Electron Accelerator
Kellogg Lab basement: E = 20 – 130 keV
Can produce 1Hz – 10 THz
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).
Ebeam = 130 keVEnergy resolution = 15%Photo-electron (pe) yield = 340 p.e./MeV
Co
un
ts
Sum of 4 PMTs
Scintillator Energy Response
Scintillator
MWPC
120 keV e- beam
Pulse Height Spectrum (Scintillator & MWPC Anode)
MWPC reconstructed position for 120 keV e- at normal incidence
Monte Carlo
Data
Anode wire spacing
z
y
Anode wires
Cathode wires
MC e-
Data e-
Anode wire spacing
x
B = 1 T
Spectrometer studies at LANSCE with 113Sn source in
1T field
Fiducial VolumeCut
Cosmic ray induced events
28Al: 2.2 min., E = 2.9 MeV endpoint
Fiducial Volume Radius 28Al -decay - via 27Al(n,)
Neutron -decay measurements in in Spectrometer
Decay Tube Radius
Room Background
Scintillator rate increases during beam pulses
First UCNA Spectrum 11/06
Signal vs Background in UCN -decay
Total background rate < 0.15 Hz
UCNA Status• All major systems commissioned• First measured -decay: 11/06 with 2 Hz• Upgrades to UCN source expected to provide
> factor 3 increase in -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 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
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.
Statitistics of UCNA
• A sensitivity:– A/A ~ 3%/month/sqrt(Hz)
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
Decay Tube
MW
PC
MW
PC
6LiF/TPX coated bore tube
6LiF/TPX UCN baffles
UCN Monitors (6LiF-coated Si)
Spectrometer
LHe plant
Pre-polarizer magnet
Polarizer AFP magnet
UCN Source
Experiment Layout
Proton Beam
CKM Summary:
New n !!
UC
NA
1% A measurement