First Measurement of the Neutron Asymmetry with Ultracold Neutrons

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R. W. Pattie, Jr.,^1,2 J. Anaya,³ H. O. Back,^1,2 J. G. Boissevain,³ T. J. Bowles,³ L. J. Broussard,^2,4 R. Carr,⁵ D. J. Clark,³ S. Currie,³ S. Du,¹ B. W. Filippone,⁵ P. Geltenbort,⁶ A. García,⁷ A. Hawari,⁸ K. P. Hickerson,⁵ R. Hill,³ M. Hino,⁹ S. A. Hoedl,^7,10 G. E. Hogan,³ A. T. Holley,¹ T. M. Ito,^3,5 T. Kawai,⁹ K. Kirch,³ S. Kitagaki,¹¹ S. K. Lamoreaux,³ C.-Y. Liu,¹⁰ J. Liu,⁵ M. Makela,^3,12 R. R. Mammei,¹² J. W. Martin,^5,13 D. Melconian,^7,14 N. Meier,¹ M. P. Mendenhall,⁵ C. L. Morris,³ R. Mortensen,³ A. Pichlmaier,³ M. L. Pitt,¹² B. Plaster,^5,15 J. C. Ramsey,³ R. Rios,^3,16 K. Sabourov,¹ A. L. Sallaska,⁷ A. Saunders,³ R. Schmid,⁵ S. Seestrom,³ C. Servicky,¹ S. K. L. Sjue,⁷ D. Smith,¹ W. E. Sondheim,³ E. Tatar,¹⁶ W. Teasdale,³ C. Terai,¹ B. Tipton,⁵ M. Utsuro,⁹ R. B. Vogelaar,¹² B. W. Wehring,⁸ Y. P. Xu,¹ A. R. Young,^1,2 and J. Yuan⁵

(UCNA Collaboration)

¹Department of Physics, North Carolina State University, Raleigh, North Carolina 27695, USA
²Triangle Universities Nuclear Laboratory, Durham, North Carolina 27708, USA
³Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA
⁴Department of Physics, Duke University, Durham, North Carolina 27708, USA
⁵W. K. Kellogg Radiation Laboratory, California Institute of Technology, Pasadena, California 91125, USA
⁶Institut Laue-Langevin, 38042 Grenoble Cedex 9, France
⁷Physics Department, University of Washington, Seattle, Washington 98195, USA
⁸Department of Nuclear Engineering, North Carolina State University, Raleigh, North Carolina 27695, USA
⁹Research Reactor Institute, Kyoto University, Kumatori, Osaka, 590-0401, Japan
¹⁰Physics Department, Princeton University, Princeton, New Jersey 08544, USA
¹¹Tohoku University, Sendai 980-8578, Japan
¹²Department of Physics, Virginia Tech, Blacksburg, Virginia 24061, USA
¹³Department of Physics, University of Winnipeg, Winnipeg, MB R3B 2E9, Canada
¹⁴Cyclotron Institute, Texas A&M University, College Station, Texas 77843, USA
¹⁵Department of Physics and Astronomy, University of Kentucky, Lexington, Kentucky 40506, USA
¹⁶Department of Physics, Idaho State University, Pocatello, Idaho 83209, USA

Received 17 September 2008; published 5 January 2009

Wereport the first measurement of an angular correlation parameter inneutron beta decay using polarized ultracold neutrons (UCN). We utilizeUCN with energies below about 200 neV, which we guide andstore for ~30 s in a Cu decay volume. The interactionof the neutron magnetic dipole moment with a static 7 Tfield external to the decay volume provides a 420 neV potentialenergy barrier to the spin state parallel to the field,polarizing the UCN before they pass through an adiabatic fastpassage spin flipper and enter a decay volume, situated withina 1 T field in a 2×2 solenoidal spectrometer. We determinea value for the beta -asymmetry parameter A₀=-0.1138±0.0046±0.0021.

URL:	http://link.aps.org/doi/10.1103/PhysRevLett.102.012301
DOI:	10.1103/PhysRevLett.102.012301
PACS:	14.20.Dh; 12.15.Ff; 12.15.Hh; 23.40.Bw 14.20.Dh Protons and neutrons 12.15.Ff Quark and lepton masses and mixing 12.15.Hh Determination of electroweak Kobayashi-Maskawa matrix elements 23.40.Bw Weak-interaction and lepton (including neutrino) aspects of β decay YEAR: 2009