Flavor (particle physics)

In particle physics, flavor is a property of a fermion that identifies it, a label that specifies the name of the particle.

According to the Standard Model, quarks exist in six flavors: up, down, charm, strange, top and bottom (indicated with the symbols u, d, c, s, t and b). Leptons occur in six other flavors: electron, muon, tau, electron neutrino, muon neutrino and tau neutrino (e⁻, μ⁻, τ⁻, ν_e, ν_μ and ν_τ). Antiparticles have −1 unit of the corresponding flavor. For example, the strange and antistrange quarks (s and ) have a strangeness of −1, and 1 respectively.

A fermion of a given flavor is an eigenstate of the weak interaction; it will interact in a definite way with the W⁺, W^- and Z bosons. On the other hand, a fermion of a fixed mass (an eigenstate of the hamiltonian) is normally a superposition of various flavors, and this gives rise to processes that change the flavor. In the case of quarks, this is reflected in the so-called CKM matrix. The equivalent for neutrinos is the MNS matrix.