Bounds on right-handed currents from nuclear beta decay

Constraints on right-handed currents are set by the precise comparison of the longitudinal polarizations PF and PGT in Fermi and Gamow-Teller β⁺ decay. Measurements with a new fourfold Bhabha polarimeter gave P_F/P_GT=1.003±0.004 with use of the matching isotopes ²⁶ᵐAl and ³⁰P. This ratio translates directly into a bound on the product of the mixing angle {ζ} and mass-squared ratio {δ} of the left- and right-handed W bosons given by -0.49×{}10³1.2 at 90% confidence.