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