In the Standard Model the idea of spontaneous symmetry breaking (see page 1047) allows particles with different masses to be viewed as manifestations of single particles, and this is effectively done for W, Z, γ, as well as for each of the 3 so-called families of quarks and leptons: u, d c, s t, b and e, v e μ, v μ τ, v τ. Real massless ones such as the photon always have just 2. Gauge bosons normally have spin 1 (the graviton would have spin 2) yielding 3 spin states for massive ones. Quarks and leptons have spin 1/2, yielding 2 spin states (neutrinos could have only 1 if they were massless). Most particles also have multiple spin states. Each quark has 3 possible color configurations the gluon has 8. Apart from the photon (and graviton), all have distinct antiparticles. Most particles exist in several variations. In ordinary matter, the only particles that contribute in direct ways to everyday physical, chemical and even nuclear properties are electrons, photons and effectively u and d quarks, and gluons. Gravitons associated with gravitational forces presumably also exist. Those currently known are the photon ( γ) for electromagnetism (QED), W and Z for so-called weak interactions, and the gluon ( g) for QCD interactions between quarks. ![]() ![]() Six types are known: u, d, c (charm), s (strange), t (top), b. Quarks exist inside hadrons like the proton and pion, but never seem to occur as ordinary free particles. The known leptons are the electron ( e), muon ( μ) and tau lepton ( τ), and their corresponding neutrinos ( n e, n μ, n τ). Current particle physics identifies three basic types of known elementary particles: leptons, quarks and gauge bosons.
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