Standard Model

Standard Model particles

Type	Generation 1	Generation 2	Generation 3
Quarks (charge +2/3)	up (u), 2.2 MeV	charm (c), 1.27 GeV	top (t), 173 GeV
Quarks (charge −1/3)	down (d), 4.7 MeV	strange (s), 95 MeV	bottom (b), 4.18 GeV
Charged leptons	electron (e), 0.511 MeV	muon (µ), 105.7 MeV	tau (τ), 1.777 GeV
Neutrinos	ν_e	ν_µ	ν_τ

Plus 12 antiparticles. Generations differ by mass; otherwise similar.

Force carriers

Force	Boson	Mass	Range
Electromagnetic	Photon (γ)	0	Infinite
Weak	W±, Z	80.4, 91.2 GeV	Very short (10⁻¹⁸ m)
Strong	Gluon (g) — 8 types	0	~1 fm (confined)
(Gravity — not in SM)	(Graviton — hypothetical)	(0)	(Infinite)

Higgs sector

Item	Value
Higgs boson mass	125.25 GeV (LHC, 2012)
Higgs field VEV	~246 GeV
Spin	0 (scalar)
Discovered	July 4, 2012; ATLAS and CMS
Nobel	Englert, Higgs (2013)

JavaScript — Standard Model summary

const SM_particles = {
  // Quarks
  'up': { type: 'quark', mass_GeV: 0.0022, charge: 2/3, generation: 1 },
  'down': { type: 'quark', mass_GeV: 0.0047, charge: -1/3, generation: 1 },
  'charm': { type: 'quark', mass_GeV: 1.27, charge: 2/3, generation: 2 },
  'strange': { type: 'quark', mass_GeV: 0.095, charge: -1/3, generation: 2 },
  'top': { type: 'quark', mass_GeV: 173, charge: 2/3, generation: 3 },
  'bottom': { type: 'quark', mass_GeV: 4.18, charge: -1/3, generation: 3 },
  // Leptons
  'electron': { type: 'lepton', mass_GeV: 0.000511, charge: -1, generation: 1 },
  'muon': { type: 'lepton', mass_GeV: 0.1057, charge: -1, generation: 2 },
  'tau': { type: 'lepton', mass_GeV: 1.777, charge: -1, generation: 3 },
  // Bosons
  'photon': { type: 'boson', mass_GeV: 0, force: 'EM' },
  'W+': { type: 'boson', mass_GeV: 80.4, force: 'weak' },
  'W-': { type: 'boson', mass_GeV: 80.4, force: 'weak' },
  'Z': { type: 'boson', mass_GeV: 91.2, force: 'weak' },
  'gluon': { type: 'boson', mass_GeV: 0, force: 'strong' },
  // Higgs
  'higgs': { type: 'scalar', mass_GeV: 125.25, role: 'mass-giver' },
};

// Group by type
const quarks = Object.keys(SM_particles).filter(p => SM_particles[p].type === 'quark');
const leptons = Object.keys(SM_particles).filter(p => SM_particles[p].type === 'lepton');
console.log('Quarks:', quarks);
console.log('Leptons:', leptons);

// Compare proton mass to constituent quarks
function protonMassFromQuarks() {
  // Proton = uud
  return 2 * SM_particles.up.mass_GeV + SM_particles.down.mass_GeV;  // GeV
}

console.log(`Proton from constituent quarks: ${protonMassFromQuarks().toFixed(4)} GeV`);
console.log(`Actual proton mass: 0.9383 GeV`);
// Most of proton mass comes from gluon binding energy, NOT quark masses
// QCD binding contributes ~99% of proton mass

// Energy scales
console.log(`Higgs VEV: 246 GeV (electroweak scale)`);
console.log(`Strong coupling at 1 GeV: ~1`);
console.log(`Strong coupling at 100 GeV: ~0.12`);
// Asymptotic freedom — strong force WEAKER at high energies

Where Standard Model matters

• Particle physics. Foundation of all collider experiments and theoretical predictions.
• Cosmology. Big Bang nucleosynthesis, baryon asymmetry, neutrino backgrounds.
• Astrophysics. Stellar evolution requires SM physics (fusion uses weak force, EM, strong).
• Material physics. Atoms work because of SM forces; chemistry is electromagnetic.
• Medicine. Particle therapy uses high-energy beam physics; PET uses positron annihilation.
• Detection technology. Particle detectors at LHC, dark matter searches, neutrino experiments.
• Open questions. SM's gaps motivate beyond-SM theories — dark matter, dark energy, hierarchy problem.

Common mistakes

• Calling SM "the theory of everything." NO — gravity is excluded. Doesn't include dark matter, dark energy. Theory of (most) everything.
• Treating quarks as separate particles. Quarks are confined inside hadrons (protons, neutrons, pions, etc.); never observed in isolation due to QCD confinement.
• Misunderstanding Higgs. Higgs gives MASS via interaction; doesn't directly cause gravity. Different physics from gravity.
• Forgetting neutrinos in SM. Often overlooked. Three neutrino flavors; recently shown to have small but nonzero masses.
• Confusing W/Z and force range. W, Z massive → short range (~10⁻¹⁸ m). Photon massless → infinite range. Gluon massless but confined → ~1 fm range.
• Mixing fundamental and composite particles. Quarks and leptons fundamental in SM; protons, neutrons, atoms are composite.