The most accurate beta asymmetry in nuclear or neutron decay:
As reported in Physical Review Letters (2018), scientists using TRINAT measured the asymmetry in the average direction of beta particles with respect to the nuclear spin of potassium-37 (37K), achieving the best fractional accuracy of any nuclear or neutron decay. Since C.S. Wu's discovery of parity violation using this observable in 1957, steadily improving experiments have shown no evidence for right-handed neutrinos. When compared to other nuclear beta decay experiments, the 37K result shows a possible 2.2 sigma discrepancy in the strength of the weak interaction in different nuclei, empirically and suggestively correlated with the density of nuclear magnetism.