quarkmass

Quark mass is a parameter in the Standard Model that characterizes the intrinsic mass of quarks, the fundamental fermions that come in six flavors. Because quarks are confined inside hadrons, their masses are not directly observable as free particles. Quark masses are defined within quantum field theory by renormalization schemes and depend on the energy scale at which they are probed. The most common schemes are the pole mass and the running MS-bar mass; the two can differ by several percent and must be converted with perturbative QCD calculations.

The six quarks span a wide range of masses. The up and down quarks are the lightest, at a few MeV. The strange quark is of order 100 MeV. The charm quark has a mass around 1.3 GeV, the bottom around 4.2 GeV, and the top around 173 GeV. In contemporary practice, masses are quoted in different schemes and at different scales: for light quarks, MS-bar masses at a reference scale (for example, m_u(2 GeV) ≈ 2–3 MeV, m_d(2 GeV) ≈ 4–5 MeV, m_s(2 GeV) ≈ 90–100 MeV); for heavy quarks, m_c(m_c) ≈ 1.27 GeV and m_b(m_b) ≈ 4.18 GeV are common MS-bar values, while the top mass is often quoted as a pole mass near 172–174 GeV.

Most of the mass of ordinary matter does not come from the intrinsic quark masses but from quantum chromodynamics binding energy and dynamics inside hadrons. Quark masses are inputs to the QCD Lagrangian and are subject to scheme- and scale-dependent definitions, making precise comparisons across contexts essential. Mass values are inferred from hadron spectra, decays, lattice QCD, and QCD sum rules.