Positron polarization in the decay of polarized 12N: a precision test of the Standard Model Original Research Article

The longitudinal polarization of positrons emitted along and opposite to the nuclear spin direction has been measured in the decay of polarized 12N. The results are consistent with the Standard Model prediction. In manifest left–right symmetric models this measurement provides a lower bound of 310 GeV/c2 at 90% CL on the mass of a possible right-handed gauge boson contributing to the electroweak interaction. In generalized versions of this model our measurement provides constraints complementary to those set by high-energy experiments.