Bounds on right-handed currents from nuclear beta decay

Constraints on right-handed currents are set by the precise comparison of the longitudinal polarizations $P_{\mathrm{F}}$ and $P_{\mathrm{GT}}$ in Fermi and Gamow-Teller ${\beta }^{+}$ decay. Measurements with a new fourfold Bhabha polarimeter gave $P_{\mathrm{F}/P_{\mathrm{GT}=1.003\mathrm{}\pm 0.004}}$ with use of the matching isotopes ${}_{}{}^{26\mathrm{m}}{}_{}{}^{}\mathrm{Al}$ and ${}_{}{}^{30}{}_{}{}^{}\mathrm{P}$. 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.