e/m Experiment Analysis Refinement

Thomson's $e/m$ experiment is widely popular in undergraduate courses to help gain an understanding of the properties of the electron. Our results using a standard apparatus, however, reveal significant systematic errors. We examine possible reasons for the discrepancy with the aim of modeling effects that were not included in the original analysis. We conclude that the energy loss of the electron beam as it travels through the helium and the distortion of the beam radius measurement by the curved glass of the tube are the two factors which dominate the discrepancy.