Search for a nonzero triple-correlation coefficient and new experimental limit onTinvariance in polarized-neutron beta decay

Abstract

A detailed description of an experimental test of time-reversal invariance in the $\ensuremath{\beta}$ decay of the polarized free neutron is presented. The experiment consists of a measurement of the triple-correlation coefficient $D$ between the neutron polarization vector and the electron and antineutrino momentum vectors. A nonzero value for this coefficient would imply $T$ violation, since final-state interactions and other corrections may be neglected at the present level of precision. The experiment was performed using a cold-neutron beam at the High Flux Reactor of the Institut Laue-Langevin, Grenoble. A polarizing neutron guide tube yielded a beam intensity of ${10}^{9}$ neutrons/sec with a polarization of 70%. Our result, based upon observation of approximately 6 \ifmmode\times\else\texttimes\fi{} ${10}^{6}$ decays, is $D=(\ensuremath{-}1.1\ifmmode\pm\else\textpm\fi{}1.7)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}3}$, consistent with time-reversal invariance in the $\ensuremath{\Delta}S=0$ weak interaction. In terms of the relative phase angle between axial-vector and vector coupling constants, the result may be expressed as $\ensuremath{\varphi}=180.14\ifmmode\pm\else\textpm\fi{}0.22\ifmmode^\circ\else\textdegree\fi{}$.

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