First measurement of the neutron β asymmetry with ultracold neutrons

R. W. Pattie, J. Anaya, H. O. Back, J. G. Boissevain, T. J. Bowles, L. J. Broussard, R. Carr, D. J. Clark, S. Currie, S. Du, B. W. Filippone, P. Geltenbort, A. García, A. Hawari, K. P. Hickerson, R. Hill, M. Hino, S. A. Hoedl, G. E. Hogan, A. T. HolleyT. M. Ito, T. Kawai, K. Kirch, S. Kitagaki, S. K. Lamoreaux, C. Y. Liu, J. Liu, M. Makela, R. R. Mammei, J. W. Martin, D. Melconian, N. Meier, M. P. Mendenhall, C. L. Morris, R. Mortensen, A. Pichlmaier, M. L. Pitt, B. Plaster, J. C. Ramsey, R. Rios, K. Sabourov, A. L. Sallaska, A. Saunders, R. Schmid, S. Seestrom, C. Servicky, S. K.L. Sjue, D. Smith, W. E. Sondheim, E. Tatar, W. Teasdale, C. Terai, B. Tipton, M. Utsuro, R. B. Vogelaar, B. W. Wehring, Y. P. Xu, A. R. Young, J. Yuan

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34 Scopus citations


We report the first measurement of an angular correlation parameter in neutron β decay using polarized ultracold neutrons (UCN). We utilize UCN with energies below about 200 neV, which we guide and store for ∼30s in a Cu decay volume. The interaction of the neutron magnetic dipole moment with a static 7 T field external to the decay volume provides a 420 neV potential energy barrier to the spin state parallel to the field, polarizing the UCN before they pass through an adiabatic fast passage spin flipper and enter a decay volume, situated within a 1 T field in a 2×2π solenoidal spectrometer. We determine a value for the β-asymmetry parameter A0=-0.1138±0.0046±0.0021.

Original languageEnglish
Article number012301
JournalPhysical Review Letters
Issue number1
StatePublished - Jan 5 2009

ASJC Scopus subject areas

  • General Physics and Astronomy


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