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Experiment Research

Experiment E07-002: Polarization transfer in Wide Angle Compton Scattering

In the early 1920s, Arthur Compton observed that if a photon strikes a charged particle, it will change direction and travel with less energy than it had before the collision. How much less energy the photon has after the collision directly depends on the angle by which the photon's path has been changed. The effect is called Compton scattering.

In Experiment E07-002, the Wide-Angle Compton scattering (WACS) experiment, scientists are observing Compton scattering to understand the structure of the proton by using electrons to generate a beam of high energy photons.

When an incoming photon scatters from the proton, the process, at low energies, depends on how the charge and magnetization distributions of the proton change in response to the photon's electric and magnetic fields. At high energies and momentum transfers, the photon sees the proton with finer resolution, so the process probes the sources of the proton's charge and magnetization distributions, the quarks.

Modern theory indicates that the high energy, high momentum transfer process proceeds largely through the photon being absorbed on a single quark, with that quark sharing momentum with the rest of the proton. However, there are several competing methods of calculating this process, each giving rise to somewhat different insights into the structure of the proton. The goal of this experiment is to test the theory calculations and therefore lead to a better understanding of the structure of the proton.

E07-002 Technical Paper (.pdf)