Measurement of Several Neutron Decay Coefficients

Alexander K. Komives (a)(b), Fred B. Bateman (b), Maynard S. Dewey (a)(b), Thomas R. Gentile (a), Jeff S. Nico (a), Alan K. Thompson (a)(b)

National Institute of Standards and Technology

W. M. Snow (a) Indiana University B.G. Yerozolimsky (b), L. Goldin (b)

Harvard University

YU.A. Mostovoy (b), S. Balashov (b)

Kurchatov Institute

R. Anderman (b), G.L. Jones (b)

Hamilton College

(a) A+B measurement , (b) "a" measurement

Neutron decay, one of the simplest examples of beta decay, is an ideal system for studying the weak interaction. The distribution of neutron decays depends on four distinct combinations of neutron spin polarization and decay product momenta. Determining the strength of this dependency on each combination yields four correlation coefficients. Improving the precision of these measurements provides increasingly stringent tests of the Electroweak Standard Model, which describes interactions between fundamental particles. Several of these coefficients are being determined at the NIST Center for Neutron Research. The development and progress being achieved on two of these experiments are described in this presentation. The first measurement determines the sum of two neutron decay coefficients, A and B. This sum is directly proportional to the asymmetry in the number of protons emitted parallel or anti-parallel to the neutron spin. A measurement of this asymmetry, which has never been successfully performed, would provide an independent method of determining the ratio of the axial vector to vector weak coupling coefficients. This ratio can be used to determine the need for extensions to the Electroweak Standard Model. Several tests and their implications on the performance of the experiment are presented. The second eperiment determines "a" - the electron-antineutrino angular correlation coefficient. A novel technique, which will circumvent some of the problems associated with earlier measurements of "a", will be utilized. An electron spectrometer that strongly suppresses backscattered electrons will be required. It is the development and testing of the prototype spectrometer and its implications for the "a" measurement that is the focus of this presentation.
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