A measurement of Aβ, the correlation between the electron momentum and neutron (n) spin (the beta asymmetry) in n beta‐decay, together with the n lifetime, provides a method for extracting fundamental parameters for the charged‐current weak interaction of the nucleon. In particular when combined with decay measurements, one can extract the Vud element of the CKM matrix, a critical element in CKM unitarity tests. By using a new SD2 super‐thermal source at LANSCE, large fluxes of UCN (ultra‐cold neutrons) are expected for the UCNA project. These UCN will be 100% polarized using a 7 T magnetic field, and directed into the β spectrometer. This approach, together with an expected large reduction in backgrounds, will result in an order of magnitude reduction in the critical systematic corrections associated with current n β‐asymmetry measurements. This paper will give an overview of the UCNA Aβ measurement as well as an update on the status of the experiment.

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