Gamma Tagging in ⁷Be Decay Measurements Using Geant-4

The BeEST experiment uses superconducting tunnel junctions (STJs) to precisely measure the nuclear recoil from the electron capture decay of ⁷Be to search for beyond standard model physics (BSM) in the neutrino sector. Recently, the first ever coincidence measurement between the nuclear recoil and the 478 keV γ-ray produced in 10% of decays to isolate the nuclear recoil spectrum from that decay branch. Improving γ tagging in future phases of the experiment will decrease the standard model-allowed background and improve the experimental sensitivity to BSM physics. This talk compares Geant-4 simulation results to our previous "nuclear recoil-gamma coincidence" measurement and presents strategies to improve future analysis and the experimental setup of the BeEST experiment.