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 $A_0=-0.1138\pm 0.0051$.

arXiv comment4 pages, 2 figures, 1 table, submitted to Phys. Rev. Lett

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• Is the Unitarity of the quark-mixing-CKM-matrix violated in neutron $\beta$-decay?
• Precision Measurements and CKM Unitarity
• Demonstration of a solid deuterium source of ultra-cold neutrons
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• Charged Current Universality in the MSSM
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Cited by in corpus (13)

• Flavor Physics in the Quark Sector
• Precision Measurement of the Neutron Beta-Decay Asymmetry
• New result for the neutron $\beta$-asymmetry parameter $A_0$ from UCNA
• Performance of the upgraded ultracold neutron source at Los Alamos National Laboratory and its implication for a possible neutron electric dipole moment experiment
• Determination of the Axial-Vector Weak Coupling Constant with Ultracold Neutrons
• Measurement of the neutron $\beta$-asymmetry parameter $A_0$ with ultracold neutrons
• Precision measurements of the ${}^{60}$Co $\beta$-asymmetry parameter in search for tensor currents in weak interactions
• Improved limits on Fierz Interference using asymmetry measurements from the UCNA experiment
• First direct constraints on Fierz interference in free neutron $\beta$ decay
• Ultracold Neutron Production in a Pulsed Neutron Beam Line
• Ultracold neutron depolarization in magnetic bottles
• Final results for the neutron $\beta$-asymmetry parameter $A_0$ from the UCNA experiment
• Happy Birthday, Ultra-Cold Neutron!