Final results for the neutron β-asymmetry parameter A₀ from the UCNA experiment

¹ University of Kentucky, Lexington, Kentucky 40506, USA
² Indiana University, Bloomington, Indiana 47408, USA
³ Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA
⁴ North Carolina State University, Raleigh, North Carolina 27695, USA
⁵ Triangle Universities Nuclear Laboratory, Durham, North Carolina 27708, USA
⁶ University of Washington, Seattle, Washington 98195, USA
⁷ Virginia Tech, Blacksburg, Virginia 24061, USA
⁸ California Institute of Technology, Pasadena, California 91125, USA
⁹ Duke University, Durham, North Carolina 27708, USA
¹⁰ Institut Laue-Langevin, 38042 Grenoble Cedex 9, France
¹¹ Kyoto University, Kumatori, Osaka, 590-0401, Japan
¹² Princeton University, Princeton, New Jersey, 08544, USA
¹³ Kyoto University, Kumatori, Osaka, 590-0401, Japan
¹⁴ Tohoku University, Sendai 980-8578, Japan
¹⁵ Shanghai Jiao Tong University, Shanghai, 200240, China
¹⁶ University of Winnipeg, Winnipeg, MB R3B 2E9, Canada
¹⁷ Texas A&M University, College Station, Texas 77843, USA
¹⁸ Idaho State University, Pocatello, Idaho 83209, USA
¹⁹ Joint Institute for Nuclear Research, 141980 Dubna, Russia

^a e-mail: brad.plaster@uky.edu

Published online: 12 December 2019

Abstract

The UCNA experiment was designed to measure the neutron β-asymmetry parameter A₀ using polarized ultracold neutrons (UCN). UCN produced via downscattering in solid deuterium were polarized via transport through a 7 T magnetic field, and then directed to a 1 T solenoidal electron spectrometer, where the decay electrons were detected in electron detector packages located on the two ends of the spectrometer. A value for A₀ was then extracted from the asymmetry in the numbers of counts in the two detector packages. We summarize all of the results from the UCNA experiment, obtained during run periods in 2007, 2008–2009, 2010, and 2011–2013, which ultimately culminated in a 0.67% precision result for A₀.