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

A detailed description of an experimental test of time-reversal invariance in the $\beta$ 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 × ${10}^6$ decays, is $D=(-1.1\mathrm{}\pm 1.7)\times {10}^{-3\mathrm{}}$, consistent with time-reversal invariance in the $\Delta S=0\mathrm{}$ weak interaction. In terms of the relative phase angle between axial-vector and vector coupling constants, the result may be expressed as $\phi =180.14\mathrm{}\pm 0.22°$.