Determination of the Weak Axial Vector Couplingλ=gA/gVfrom a Measurement of theβ-Asymmetry ParameterAin Neutron Beta Decay

We report on a new measurement of the neutron $$\beta${}$-asymmetry parameter $A$ with the instrument Perkeo II. The main enhancements are the high neutron polarization of $P=99.7(1)%$ from a novel arrangement of supermirror polarizers and reduced background from improvements in beam line and shielding. The leading corrections were thus reduced by a factor of 4, pushing them below the level of statistical error and resulting in a significant reduction of systematic uncertainty compared to our previous experiments. We derive the $$\beta${}$-asymmetry parameter ${A}_{0}=-0.11972(45{)}_{\mathrm{stat}}{(}_{-44}^{+32}{)}_{\mathrm{sys}}=-0.11972{(}_{-65}^{+53})$ and the ratio of the axial vector to the vector coupling constant $$\lambda${}={g}_{A}/{g}_{V}=-1.2761(12{)}_{\mathrm{stat}}{(}_{-12}^{+9}{)}_{\mathrm{sys}}=-1.2761{(}_{-17}^{+14})$.