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

Abstract

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 $\lambda =g_A/g_V=-1.2761(12{)}_{\mathrm{stat}}{(}_{-12}^{+9}{)}_{\mathrm{sys}}=-1.2761{(}_{-17}^{+14})$. DOI: http://dx.doi.org/10.1103/PhysRevLett.110.172502 © 2013 American Physical Society