Positron-Neutrino Correlation in the0+→0+Decay of32Ar

The positron-neutrino correlation in the $0^{+}\to 0^{+}$ $\beta$ decay of ${}^{32}\mathrm{Ar}$ was measured at ISOLDE by analyzing the effect of lepton recoil on the shape of the narrow proton group following the superallowed decay. Our result is consistent with the standard model prediction. For vanishing Fierz interference we find $a=0.9989\mathrm{}\pm 0.0052\pm 0.0039$, which yields improved constraints on scalar weak interactions.