Particles, such as quarks, are indeed not solid objects in the traditional sense. They are elementary particles that are described by quantum field theory. In experiments performed at the Large Hadron Collider (LHC) or any other particle collider, the collisions occur at the subatomic level, where the particles involved are treated as point-like entities.
The LHC accelerates particles, such as protons or lead ions, to extremely high speeds using powerful electric and magnetic fields. These particles are then directed into collision courses with each other. While the particles themselves do not physically collide like solid objects, their constituent quarks and gluons (in the case of protons) can interact with each other through the fundamental forces of nature.
In the context of quantum field theory, particles are represented as excitations of their respective fields. When two particles collide at high energies, their fields interact, and the particles involved can exchange energy and momentum. This interaction is described by mathematical formulas known as scattering amplitudes, which provide the probabilities of different outcomes resulting from the collision.
The LHC detectors are designed to measure the particles produced after the collisions. These detectors record the trajectories, energies, and other properties of the particles emerging from the collision point. By analyzing these measurements, scientists can reconstruct the dynamics of the collision and study the fundamental particles and forces that govern the behavior of matter at the smallest scales.
So, while particles like quarks are not solid, their interactions and collisions can be described and studied within the framework of quantum field theory and the mathematical formalism of particle physics.