Compton Polarimetry in the Electron-Ion Collider

Electron polarimetry is to be an essential part of the next-generation nuclear facility, the Electron-Ion Collider (EIC). The EIC will facilitate the detailed study of the internal structure of the proton by creating high-energy interactions between a stream of electrons and a stream of deshielded protons. To interpret these interactions, the polarization of the electron beam must be known. Accordingly, a Compton polarimeter will be stationed within the EIC to measure and monitor the polarization of the electron beam by colliding photons with the electron beam to produce Compton scattering. The physical quantities measured in the scattering will correlate to the electron beam's degree of polarization, rendering the polarization calculable. A fast- pulse laser system will be used in this process, since the EIC necessitates that polarization measurements be significantly more accurate than 1%. To determine properties of the laser to be used, an autocorrelator was designed and assembled for pulse measurement. The autocorrelator splits the original pulse into two identical beams which are then superimposed with variable temporal difference. Though the pulse duration is not directly observed, measurable signals are produced from the interactions, allowing it to be calculated. Since the sensitivity of the polarimeter largely depends on the properties of the electron and photon beams, simulation studies were also performed. Three simulations of Compton interactions were produced: the first assumed infinitely focused beams, while the second assumed a realistic electron beam size and a large laser beam size, and the third assumed a realistic electron beam size and a realistic laser beam size. The impact on the sensitivity of the system was analyzed via these simulations, the results of which proved the proposed laser system adequate.