Background characterization and calibrations of SiPM detectors for UCNA+

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 % on A₀. 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 and minimizing scattering on inactive material. A completed prototype was installed in the spectrometer at LANL in December to measure and characterized ambient and accelerator generated backgrounds in Area B. We will report on the tests of the data acquisition system, trigger logic, background rejection, and calibration of the prototype detectors.