First Measurement of the Neutron $\beta$-Asymmetry with Ultracold Neutrons

Abstract

We report the first measurement of angular correlation parameters in neutron $\beta$-decay using polarized ultracold neutrons (UCN). We utilize UCN with energies below about 200 neV, which we guide and store for $\sim 30$ s in a Cu decay volume. The ${\vec{\mu }}_n\cdot \vec{B}$ potential of 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 (AFP) spin-flipper and enter a decay volume, situated within a 1 T, $2\times 2\pi$ superconducting solenoidal spectrometer. We determine a value for the $\beta$-asymmetry parameter $A_0$, proportional to the angular correlation between the neutron polarization and the electron momentum, of $A_0=-0.1138\pm 0.0051$.

4 pages, 2 figures, 1 table, submitted to Phys. Rev. Lett

References in corpus (4)

• Tests of the standard electroweak model in beta decay
• Experiments in Fundamental Neutron Physics
• A solenoidal electron spectrometer for a precision measurement of the neutron $\beta$-asymmetry with ultracold neutrons
• A Multiwire Proportional Chamber for Precision Studies of Neutron Beta Decay Angular Correlations