Simulation Studies of the Aluminum Grid Wire Effect on Proton Detection Efficiency in the Nab Experiment

The Nab Experiment’s primary objective is to study the process of unpolarized neutron beta decay using the Spallation Neutron Source at Oak Ridge National Laboratory. Specifically, we plan to measure two values: a, the electron-neutrino correlation coefficient to a precision of δa/a ≤ 10^-3 and the Fierz interference term, b, to δb ≈ 3 × 10^-3 .The experimental set-up includes two silicon detectors on either end of a large electromagnetic spectrometer that will detect the proton and electron decay products. Each detector is covered with a grid of thin aluminum wires with a spacing of 4 mm over the active areas. These wires are necessary to maintain a uniform electrostatic potential across the detectors. Using Geant4, we are investigating the impact the grid wires have on the upper detector’s ability to detect the protons, as well as how they might contribute to our uncertainty in the measurement of the parameter a. We will give an overview of the simulation project and report our findings.