Compton Scattering Cross Section Measurement in Hall D at Jefferson Lab

The PrimEx-Eta fixed-target experiment in Hall D at Jefferson Lab 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 data taking of the first two phases of the PrimEx-Eta experiment were completed in Spring 2019 and Fall 2021, with the majority of the data being collected on a liquid ⁴He target. In this talk, I will discuss the preliminary results for the total Compton scattering cross section measured on both the liquid ⁴He target, as well as a solid ⁹Be target. Our result will offer the first measurement on this fundamental QED process with a beam energy up to 10 GeV. I will also present the systematic uncertainties associated with this cross section measurement and discuss how it will be utilized in the η meson decay width measurement.