Quarks are elementary particles that are considered to be the fundamental building blocks of matter. According to the current understanding of particle physics, quarks do have mass. However, the masses of quarks are relatively small compared to other particles, such as the proton or neutron, which are composed of quarks.
The masses of quarks are not directly measured as isolated particles because they are always confined within composite particles due to a fundamental interaction called the strong nuclear force. This confinement is described by a theory called quantum chromodynamics (QCD), which is a part of the Standard Model of particle physics.
In QCD, quarks are bound together by exchanging gluons, the carriers of the strong force. The confinement of quarks means that they cannot be observed as isolated particles but are always found within composite particles called hadrons, such as protons and neutrons.
The masses of quarks are determined indirectly through experiments and theoretical calculations based on the properties and behavior of hadrons. These calculations involve complex techniques such as lattice QCD simulations and experimental data from particle colliders.
It's worth noting that the masses of quarks are not solely responsible for the mass of a composite particle like a proton. The masses of quarks, the binding energy, and the contributions from the Higgs mechanism all play a role in determining the overall mass of composite particles.