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/PGT=1.003±0.004 with use of the matching isotopes 26m Al and 30 P. 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<δζ×10 3 <1.2 at 90% confidence