Initial Asymmetry Results from the UCNA Experiement

In the decay of free polarized neutrons, there is an asymmetry in the emission direction of electrons with respect to neutron spin, which is related to $\lambda$, the ratio of the axial-vector and vector coupling constants. By measuring this asymmetry and the neutron lifetime, it is possible to determine $V_{ud}$, the first element of the CKM matrix. The UCNA collaboration will be the first to measure this asymmetry using ultra-cold neutrons, which allow for nearly $100\%$ polarization and transport far from the source to reduce backgrounds. In 2007, all major systems required for a high precision measurement of the neutron beta-asymmetry were commissioned and a measurement with $\approx 3\%$ statistical uncertainty was performed. Analysis of these initial results will be presented.