= Solution
<parity> reverses spatial coordinates and <polar vectors> such as <momentum>, while leaving <axial vectors> such as <angular momentum> unchanged. The correlation $\mathbf J\cdot\mathbf p_e$ is therefore <parity> odd. For polarized beta-emitting <nuclei> one can measure
$$
W(\theta)\propto1+A\mathcal P\frac vc\cos\theta,
$$
where $\theta$ is measured from <nuclear polarization>, $\mathcal P$ its magnitude and $A$ a decay-dependent coefficient. A nonzero <spin>–<momentum> asymmetry is incompatible with <parity> invariance.
The <cobalt-60> experiment polarized <nuclei> at low temperature and compared beta emission along and opposite the polarization axis. Preferential emission on one side established weak-interaction <parity violation>. Reversing polarization tests whether the asymmetry follows nuclear orientation; warming the sample removes polarization, while gamma anisotropy monitors its loss. Detector acceptance, backgrounds and magnetic deflection of charged particles must be separated from a true emission asymmetry.<Experimental Test of Parity Conservation in Beta Decay by Chien-Shiung Wu and others>[1957, polarized cobalt-60 experiment and temperature/polarization checks]{ref}
In the modern <weak charged current>, the <V-A interaction> couples to left-chiral <fermion> fields. In the massless limit this selects left-helicity <neutrinos> and right-helicity <antineutrinos>. Massive charged <leptons> need not be pure-helicity states, consistent with the factor $v/c$. Strong and <electromagnetic interactions> conserve <parity> to the usual experimental approximation; <parity violation> alone should not be confused with <CP violation> or a failure of CPT.
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