In a particle accelerator, such as the Large Hadron Collider (LHC), the individual quarks themselves do not have a single, well-defined velocity. Quarks are fundamental particles that are permanently confined within composite particles, such as protons and neutrons, due to a phenomenon known as color confinement.
In the context of particle accelerators, what is typically measured is the velocity of the composite particles, rather than the individual quarks. The composite particles, such as protons or lead nuclei, are accelerated to very high speeds within the accelerator. In the LHC, for example, protons are accelerated to velocities close to the speed of light, specifically about 99.9999991% of the speed of light.
It's important to note that the velocity of particles in a particle accelerator can be different from the velocities of the quarks within those particles. The velocity of quarks within a composite particle depends on a variety of factors, including the energy of the quarks, their interaction with other quarks, and the overall properties of the composite particle itself.