In SpinQuest, protons will be fired at a polarized target, shown here. Scientists will measure two different angles related to the particles that result from the beam-target interaction: the angle between a flat surface formed from the resulting particle tracks and the orientation of the target proton’s spin when it points up, and another angle when the target proton’s spin points down. The angle is connected to how the sea quarks contribute to proton spin. Photo: Reidar Hahn, Fermilab