Speaker
Description
The $\beta$-decay of the free neutron contains a wealth of information about the charged weak interaction. Measurements of the lifetime and angular correlation coefficients can be use to determine $V_{ud}$, the first element of the Cabibbo–Kobayashi–Maskawa quark mixing matrix.Traditionally Super-allowed Fermi nuclear beta-decays have provided the most precise determination of $V_{ud}$, but modern neutron experiments are poised to generate results with similar or better precision. Having these two complementary determinations will provide a powerful tool to probe for physics beyond the standard model. The UCN$\tau$ experiment at the Los Alamos Ultracold Neutron facility has completed a $\approx 0.03$ % measurement of the neutron lifetime using a magneto-gravitational trap with {\it in situ} neutron detection, $\tau_n = 877.75(0.28)_{stat}(0.22)_{syst}$ s. Ultracold neutrons are stored for up to 5000~s and the surviving neutrons are counted to determine the decay lifetime. The trap eliminates material interactions during the storage period and its asymmetric shape is designed to remove super-barrier neutrons in stable orbits. As a cross check of the {\it in situ} counting method a recent measurement emptied the trap to an external detector after storage resulting in a value of $\tau_n = 877.1 (2.6)_{stat}(0.8)_{syst}$ s. Future upgrades are expected to push the precision of UCN$\tau$ to $\leq 0.1$ s. The results of these recent measurements and the path towards a 0.1~s precision on $\tau_n$ will be presented.
