UCNA+: A precision measurement of the beta-asymmetry with ultracold neutrons

The UCNA experiment at the Ultracold neutron facility at Los Alamos National Lab measured the beta-asymmetry parameter A₀ to a precision of 0.6%. This parameter is used in determinations of the ratio of the axial and vector weak coupling constants and combined with measurements of the neutron lifetime is used to test the unitarity of the CKM quark mixing matrix and beyond the standard model physics searches. Upgrades of several key subsystems of UCNA are being investigated with the goal of reaching a precision of 0.2% in A₀. Upgrades of several key subsystems of UCNA will enable systematic uncertainties related to scattering and polarization to be reduced are in development. The statistical sensitivity will be enhanced due to the recent upgrade of the LANL ultracold neutron source. A prototype of the electron detector is in development which would eliminate the MWPC gas counter and traditional PMT's in favor of an array of edge-coupled SiPM's. The SiPM array will provide energy, position, and timing data with resolution that is equal to or better than the original detector. This change will reduce systematic uncertainties that arose from scattering on the inactive material in the MWPC. We will present the status of the upgrade to UCNA and the development of a prototype detector array.