The quantum nature of interactions between elementary particles allows drawing non-trivial conclusions even from processes as simple as elastic scattering. The ATLAS experiment at the LHC accelerator reports the measurement of fundamental properties of strong interactions between protons at ultra-high energies.
The physics of billiard ball collisions is taught from early school years. In a good approximation, these collisions are elastic, where both momentum and energy are conserved. The scattering angle depends on how central the collision was (this is often quantified by the impact parameter value—the distance between the centers of the balls in a plane perpendicular to the motion). In the case of a small impact parameter, which corresponds to a highly central collision, the scattering angles are large. As the impact parameter increases, the scattering angle decreases.
In particle physics, we also deal with elastic collisions, when two particles collide, maintaining their identities, and scatter a certain angle to their original direction of motion. Here, we also have a relationship between the collision parameter and the scattering angle. By measuring the scattering angles, we gain information about the spatial structure of the colliding particles and the properties of their interactions.
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