Simulations of Proton Tacking and Detector Performance in the BL3 Experiment

Neutron beta decay is one of the most fundamental processes in nuclear physics and provides sensitive means to uncover the details of the weak interaction. A precise measurement of the neutron lifetime, along with neutron beta decay correlations, can provide tests of CKM unitarity and is needed for BBN models of the primordial 4He abundance. A next generation beam method experiment, BL3 at the NCNR, aims to improve the systematic precision of neutron lifetime measurements in order to resolve the discrepancy between beam and bottle method measurements. In BL3, the recoil protons from neutron beta decay are born in a quasi-Penning trap with magnetic and electric fields which transport them to a segmented silicon detector. The BL3 experiment will use higher neutron flux in a larger beam, which requires a larger proton detector than the BL2 experiment. The BL3 collaboration is using a combination of simulation tools to assess the anticipated performance. Simulations in Geant4 and Kassiopeia have been developed which use different electric and magnetic field propagation, as well as different physics lists for low-energy interactions. Additionally, a study of backscattering will be discussed. We will present results obtained with these different approaches to assess the performance of the BL3 apparatus.