Compton Scattering Cross Section Measurement in Hall D at Jefferson Lab*

The PrimEx-Eta fixed-target experiment in Hall D at Jefferson Lab (E12-10-011) will measure the η→γγ decay width using the Primakoff method with a projected uncertainty of 3.2%. In order to achieve this goal, Compton scattering from the atomic electrons in the target is being used as a reference process. Because of its similar kinematics to the η→γγ decay, the total Compton scattering cross section can be measured using the same experimental configuration as the η decay width measurement. Thus, it can be used to verify the systematic uncertainties for the η decay width measurement and monitor the luminosity, detection efficiency, and overall experimental stability. The first phase of the PrimEx-Eta data was collected in 2019, corresponding to roughly one-third of the total proposed statistics. In this talk, I will discuss the preliminary results for the total Compton scattering cross section measured on a ⁹Be target as well as a liquid ⁴He target.