Geant4 simulations of electron detection systematic errors for UCNA+ experiment.

Significant research and development has been undertaken for the UCNA+ experiment, which is a proposed upgrade of the previous UCNA(Ultra Cold Neutron Asymmetry) experiment conducted at Los Alamos National Laboratory. The primary objective of UCNA+ would be to measure the neutron beta-asymmetry A₀, which quantifies the correlation between the spin of the polarized neutron and the decay beta-particle, with a precision of less than $0.2\%$. To achieve this, UCNA+ will implement several improvements including an upgraded high-density ultracold neutron (UCN) source to enhance the statistical precision, improved detection techniques utilizing silicon photomultipliers (SiPMs), and effective reduction of electron backscattering. This talk reports on outcomes obtained through Monte Carlo simulations using Geant4 for the experimental setup of UCNA+. Specifically, we define (through Monte Carlo studies) a set of scattering measurements on the ultrathin foils used in the UCNA experiment which can directly characterize the effects of backscatter and energy loss expected for UCNA+. These measurements would be performed using conversion electron sources mounted in the UCNA spectrometer and the upgraded detector packages proposed for UCNA+. The expected accuracy of our models for scattering and the resultant uncertainties for the upgraded asymmetry experiment are explored by specifying the expected scattering effects for measurements using several conversion electron sources, thicknesses of backing foil for these sources, and various configurations for ultrathin foils used in the asymmetry measurement. Additionally, we compare different physics models employed in the simulations and investigate the influence of source positioning on the observed outcomes.

The analysis of this work will be presented.

This material is based upon work supported by the U.S. Department of Energy, Office of Science, Office of Nuclear Physics, under Award Number DE-SC0014622.