Determination of the Weak Axial Vector Coupling from a Measurement of   the Beta-Asymmetry Parameter A in Neutron Beta Decay
  We report on a new measurement of the neutron beta-asymmetry parameter $A$ with the instrument \perkeo. Main advancements are the high neutron polarization of $P = 99.7(1)%$ from a novel arrangement of super mirror polarizers and reduced background from improvements in beam line and shielding. 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. From the result $A_0 = -0.11996(58)$, we derive the ratio of the axial-vector to the vector coupling constant $\lambda = g_\mathrm{A}/g_\mathrm{V} = -1.2767(16)$ 
D. Mund, B. Maerkisch, M. Deissenroth, J. Krempel, M. Schumann, H.   Abele, A. Petoukhov, T. Soldner
hep-ex nucl-ex