UCNA Results and Prospects for Improvement: Update on High Precision Polarimetry and the Beta Asymmetry

The UCNA experiment determines the axial coupling constant in neutron decay, critical input for a high precision characterization of the charged weak current from neutron decay, through a measurement of the beta asymmetry in polarized ultracold neutron(UCN) decay.  We present an update on the analysis of the 2011-2013 UCNA runs, primarily through an expanded Monte Carlo analysis of polarization and polarimetry. We summarize the current status of UCNA and update our assessment of the systematic error budget, and compare to previous geometries associated with 2008-2010 datasets.  Our new analysis provides insight into the management of systematic errors for the UCNA geometry in the 2011-2013 run cycle and for future upgrades of the experiment, made possible by recent progress at the LANL Area B UCN source increasing the available UCN density by a factor of 4 to 5 (depending on experimental details).