The velocity of quarks in a particle accelerator depends on several factors, such as the type of accelerator, the energy of the particles, and the specific experiment being conducted. However, it's important to note that quarks cannot be observed as free particles due to a property called confinement, which means they are always bound together inside composite particles such as protons and neutrons.
In a particle accelerator, quarks are typically accelerated to very high energies within these composite particles. The composite particles, also known as hadrons, are then accelerated to high velocities. The velocity of the hadrons in a particle accelerator is usually very close to the speed of light, which is approximately 299,792,458 meters per second in vacuum.
It's worth mentioning that the velocity of quarks themselves is not directly measured or known in the context of a particle accelerator. Instead, scientists focus on the properties and interactions of the composite particles that contain quarks, using the accelerators to study their behavior at high energies and speeds.