Title: Measurement of Acorrelation in decay of UCN
1Measurement of A-correlation in?-decay of UCN
Jeff Martin UCN A Collaboration
- W. K. Kellogg Radiation Laboratory
- California Institute of Technology
2Neutron ?-decay
measuring e.g.
allows extraction of GV and GA
Taking GF from ?-decay allows extraction of
Vud and test of CKM unitarity.
GV most precisely obtained from 0?0
nuclear ?-decay (nuclear correction)
3Experimental Status
- Discrepancy between 0?0 nuclear ?-decay
measurements and CKM unitarity - Large spread among A measurements using cold
neutrons
4Experimental Method
Endpoint energy 782 keV
Focus electrons onto detectors using a strong (1
T) magnetic field
5Ultracold Neutrons
- Neutrons that undergo total external reflection
from a variety of materials - Can be confined in material bottles for long
periods of time - Typically
- velocity lt 8 m/s
- temperature lt 4 mK
- kinetic energy lt 300 neV
- Strongly affected by
- gravity 100 neV/m
- magnetic fields 100 neV/1.7 T
- UCN confined by effective Fermi potential built
up from low-energy n-nucleus scattering. 58Ni
has highest known potential (335 neV) - conventionally produced by cooling reactor
neutrons
6Desired Improvements in A
- Previous A measurements done with cold neutron
beams from reactors, and used supermirror
polarizers. - Using UCN, expect
- reduced backgrounds
- pulsed spallation source, low loss UCN transport
over meters - higher neutron polarization
- UCN 100 polarized by passage through strong B
field
7The UCN A Experiment
California Institute of Technology R. Carr, B.
Filippone, T. M. Ito, J.W. Martin, R. McKeown, B.
Tipton, J. Yuan Institut Laue-Langevin P.
Geltenbort Japan Atomic Energy Research
Institute K. Soyama Los Alamos National
Laboratory T. Bowles (co-PI), M. Fowler, R. Hill,
A. Hime, G. Hogan, K. Kirch, S. Lamoreaux, C.
Morris, A. Pichlmaeir, A. Saunders, S. Seestrom,
P. Walstrom, J. Wilhelmy University of Notre
Dame A. Garcia, E. Tatar North Carolina State
University G. Dodson, F. Dudziak, Y.P. Xu, A.R.
Young (co-PI) Petersburg Nuclear Physics
Institute A. Alduschenkov, A. Kharitonov, M.
Lassakov, Yu. Rudnev, A. Serebrov, A.
Vasilev Princeton University S. Hoedl, C-Y.
Liu Tohoku University T. Kitagaki Tokyo Institute
of Technology K. Asahi University of Kyoto M.
Hino, T. Kawai, M. Utsuro Virginia Polytechnic
Institute and State University M. Makela, M.
Pitt, R.B. Vogelaar
8Los Alamos Neutron Science Center LANSCE
Linac
UCN
9Layout in Area B
800 MeV protons
Cryogenics Systems
UCN Source
Polarized and unpolarized neutron guides
Polarizer/AFP
Superconducting Spectrometer (SCS)
Analyzer
10Solid D2 Spallation UCN Source
- source is pulsed to reduce backgrounds
- prototype source used to characterize
neutronics of SD2 (nucl-ex/0109020) and produce
new world-record UCN density
Be
Tungsten target
11Prototype UCN Source
nucl-ex/0109020
12Polarizer/AFP
- 7 T field only passes one spin state of UCN
(P100) - Adiabatic Fast Passage (AFP) resonator allows
spin reversal. - Prototype tested during ILL depolarization
measurements AFP efficiency gt 99
13Polarized Neutron Guides
Pulsed Laser Deposition (PLD) of diamond onto
glass tubing
Critical Velocity gt 6.7 m/sDepolarization
2 x 10-6/collisionRoughness RA
? 0.15 nm
14ILL Depolarization Measurement
Institut Laue-Langevin Grenoble, France
- results
- depol/bounce 2?10-6
- AFP prototype
- efficiency gt 99
15Experiment
16Spectrometer
1 Tesla Central Field
Neutron Storage Cell
Decay Electron Detectors
17Detector Installation
- option to use silicon multi-strip (better energy
resol.) - prototypes complete, entering construction phase
18Experimental Parameters
- Goal precision ?A/A 0.2
- collection of 2?108 decays
- Decay rate 100 Hz, 21 days data-taking
- UCN polarization gt 99.9 determined to 0.1
- Depolarization limited to 0.1 by holding UCN 6
seconds - Signal/background 220/1, background mainly from
UCN in spectrometer
Dominant systematic corrections
Extensive detector calibration scheme and new
measurements of electron backscattering
19Calibration Sources
JPL Dynamitron 0.2-1 MeV
Also, standard ? and CE sources and radioactive
Xe
Kellogg Electron Gun 0-0.15 MeV
20Helmholtz-Coil Spectrometer
J. Yuan et al, NIM A465(2001)404
- Results
- resolution ?p/p0.3
- energy calibration to 0.1 of both gun and
dynamitron
21Possibilities for B and a
- measurement of proton emission asymmetry, proton
spectrum gives sensitivity to B and a,
respectively
- exploring thin films coated with MgO, CsI,
diamond, - can be incorporated into UCN A setup
- has minimal effect on electron transport
extraction of B at 0.1 level for 2?107
decays extraction of a at 0.3 level for 4?108
decays
22Expected Precision
23Theory Corrections
- Radiative corrections
- definition of effective coupling
constants 2.40(8) - difference in RC for ?n and A 0.1
- Recoil-order corrections
- Weak magnetism ?a 1
- Induced tensor gT 0.0(1)
- can be extracted from E-dependence of A
(c.f. experiment precision 0.2)
24Right-Handed Currents
- Projected sensitivity for right-handed currents
for UCN A - Neutron present limits taken from Particle Data
Group compilation - 19Ne result is the most recent Princeton
measurement - muon is PSI meast
- muon projected is TWIST
muon (projected)
25Supersymmetry
Sensitive to loop corrections ?-decay sensitive
to differences in squark/slepton couplings
Interesting question What if UCN A measures
PERKEO II mean value?
26MSSM
Kurylov and Ramsey-Musolf PRL88(2001)076007
Size of corrections needed to account for data
(?-decay, g-2?) are too small or lead to
contradictions. e.g.
Squark Non-Universality
But mSUGRA and gauge-mediated SUSY-breaking
models give
27R-Parity Violating SUSY
Ramsey-Musolf PRD62(2000)056009
Effective 4-fermi coupling gives RC at low
energy, e.g.
Take model where and and all
other
Both contribute to ?-decay and APV in different
ways. Cannot be ruled out by existing data.
28Schedule
- Experiment fully funded, in construction phase
- Polarizer/AFP Apr. 2002
- Full UCN Source Fall 2002
- Detector tests with source Fall 2002
- Spectrometer magnet Feb. 2003
- Preliminary runs Spring 2003
- Production running Summer 2003