Measurement of Acorrelation in decay of UCN

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Measurement of A-correlation in?-decay of UCN
Jeff Martin UCN A Collaboration

• W. K. Kellogg Radiation Laboratory
• California Institute of Technology

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Neutron ?-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)
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Experimental Status

• Discrepancy between 0?0 nuclear ?-decay
  measurements and CKM unitarity
• Large spread among A measurements using cold
  neutrons

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Experimental Method
Endpoint energy 782 keV
Focus electrons onto detectors using a strong (1
T) magnetic field
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Ultracold 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

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Desired 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

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The 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
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Los Alamos Neutron Science Center LANSCE
Linac
UCN
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Layout in Area B
800 MeV protons
Cryogenics Systems
UCN Source
Polarized and unpolarized neutron guides
Polarizer/AFP
Superconducting Spectrometer (SCS)
Analyzer
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Solid 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
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Prototype UCN Source
nucl-ex/0109020
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Polarizer/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

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Polarized 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
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ILL Depolarization Measurement
Institut Laue-Langevin Grenoble, France

• results
• depol/bounce 2?10-6
• AFP prototype
• efficiency gt 99

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Experiment
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Spectrometer
1 Tesla Central Field
Neutron Storage Cell
Decay Electron Detectors
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Detector Installation

• option to use silicon multi-strip (better energy
  resol.)
• prototypes complete, entering construction phase

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Experimental 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
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Calibration Sources
JPL Dynamitron 0.2-1 MeV
Also, standard ? and CE sources and radioactive
Xe
Kellogg Electron Gun 0-0.15 MeV
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Helmholtz-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

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Possibilities 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
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Expected Precision
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Theory 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)
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Right-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)
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Supersymmetry
Sensitive to loop corrections ?-decay sensitive
to differences in squark/slepton couplings
Interesting question What if UCN A measures
PERKEO II mean value?
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MSSM
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
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R-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.
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Schedule

• 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