Limits on nonstandard weak currents from the polarization of ¹⁴O and ¹⁰C decay positrons

We report the relative polarization of the P_F/P_GT=0.9996±0.0037 for the positrons emitted by the pure Fermi ¹⁴O and the pure Gamow-Teller ¹⁰C decays, using a technique based on the observation of the positronium-decay time spectrum. The radioisotopes to be compared are part of the same source, eliminating some of the potential systematic errors which may vitiate relative polarization measurements of high precision. Combining our result with a similar ²⁶Al^m/³⁰P decay positron comparison obtained by Bhabha polarimetry, we deduce the following constraint on the product of the mixing angle ζ and mass-squared ratio δ of the chiral W bosons assumed in left-right symmetric models: -0.0004<ζδ<0.0007 (90% C.L.). Our result also constrains possible scalar and tensor admixtures to the dominant vector and axial-vector currents: C_S+C’_S/C_V-C_T+C’_T/C_A =0.003±0.018 (90% C.L.).