New result for the neutron $\beta$-asymmetry parameter $A_0$ from UCNA

The neutron $\beta$-decay asymmetry parameter $A_0$ defines the correlation between the spin of the neutron and the momentum of the emitted electron, which determines $\lambda =\frac{g_A}{g_V}$, the ratio of the axial-vector to vector weak coupling constants. The UCNA Experiment, located at the Ultracold Neutron facility at the Los Alamos Neutron Science Center, is the first to measure such a correlation coefficient using ultracold neutrons (UCN). Following improvements to the systematic uncertainties and increased statistics, we report the new result $A_0 = -0.12054(44){$\mathrm{s}\mathrm{t}\mathrm{a}\mathrm{t}$}(68){$\mathrm{s}\mathrm{y}\mathrm{s}\mathrm{t}$}$whichyields$\lambda\equiv \frac{g_{A}}{g_{V}}=-1.2783(22)$. Combination with the previous UCNA result and accounting for correlated systematic uncertainties produces $A_0=-0.12015(34{)}_{\mathrm{s}\mathrm{t}\mathrm{a}\mathrm{t}}(63{)}_{\mathrm{s}\mathrm{y}\mathrm{s}\mathrm{t}}$ and $\lambda\equiv \frac{g_{A}}{g_{V}}=-1.2772(20)$.