What is Leptons, quarks, hadrons? — Physics

Definition 26.1 University Physics — Year 3 · Chapter 26 — Particle Physics

Matter’s building blocks are spin- $\tfrac12$ fermions (Chapter 12, Chapter 14) in two families of six. Leptons feel no strong force: the electron, muon and tau (charge $-e$ , each heavier than the last) and their three neutrinos — nearly massless, nearly undetectable. Quarks come in six flavours — up, down, strange, charm, bottom, top — with charges $+\tfrac23e$ (u, c, t) and $-\tfrac13e$ (d, s, b), and they are never seen alone: confinement binds them into hadrons — three-quark baryons (proton $=$ uud, neutron $=$ udd) and quark–antiquark mesons (pion, kaon). Each particle has an antiparticle of identical mass and opposite charges (Exercise 26.8). Ordinary matter uses only the first generation — u, d, e, $\nu_{\text{e}}$ ; the two heavier copies differ, as far as anyone knows, only in mass. “Who ordered that?” physics still asks.

The Standard Model roster (charges in units of e). One column of it builds every atom; the other two are expensive echoes. Gravity, feeble beyond measure at these masses, has no seat at the table — the model’s most famous vacancy. — The Standard Model roster (charges in units of $e$ ). One column of it builds every atom; the other two are expensive echoes. Gravity, feeble beyond measure at these masses, has no seat at the table — the model’s most famous vacancy.

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