Phys. Rev. Lett. 102, 012301 (2009) [4 pages]First Measurement of the Neutron β Asymmetry with Ultracold NeutronsReceived 17 September 2008; published 5 January 2009 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 ∼30 s 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. © 2009 The American Physical Society 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
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