Monte Carlo Simulations of Nab & BL3*

Neutron beta decay is the fundamental process that Nab and BL3 aim to understand more precisely. The

main objective of Nab and BL3 is to precisely test Vud unitarity of the CKM matrix in the standard model.

If the CKM matrix is not unitary, there may be physics beyond the standard model. In order to derive Vud

the neutron lifetime and the decay correlations in neutron beta decay is needed. There are two methods to

measure the neutron lifetime, the beam method and the bottle method. BL3 is a next generation beam line

experiment proposed in order to resolve the 4σ (10s) discrepancy between the beam and bottle method by

improving the systematic precision for the beam method. In this presentation we will show Monte Carlo

simulation data that looks into the effect that backscattering protons have on systematic errors. Nab aims

to measure the decay correlation angle ”a” by utilizing unpolarized neutron beta decay. We will also present

kinetic energy distributions that are made with Monte Carlo methods with and without radiative effects in

neutron beta decay. These results will be propagated through the Nab and BL3 Monte Carlo simulation

packages.