# Particle Physics Particle physics asks what everything is made of at the smallest scale, and what holds it together. The answer is the **Standard Model**: a short list of elementary particles and three of the four known forces, written in the language of relativistic quantum fields. _Figure 001 — A Feynman diagram: an electron and positron annihilate into a virtual photon, which becomes a muon–antimuon pair. _ _Figure 002 — The Standard Model: three generations of quarks and leptons, the gauge bosons, and the Higgs. _ Matter is built from two families — **quarks** and **leptons** — each appearing in three generations of rising mass. The forces are carried by _gauge bosons_: the gluon, the photon, and the massive _W_ and _Z_. Every prediction runs through the same machinery. A process is a sum of **Feynman diagrams**, each vertex a factor and each internal line a virtual particle, and the calculus turns those pictures into rates and cross-sections you can measure. _Figure 003 — Colliders test it: beams meet head-on and the energy sprays out as jets reconstructed back to the vertex. _ The strong force is stranger than gravity or electromagnetism. Its charge, _colour_, grows more binding with distance, so quarks are permanently **confined** inside hadrons and never seen alone. _Figure 004 — Confinement: stretch a quark pair and the flux tube snaps into a new pair rather than releasing a free quark. _ The weak force and electromagnetism are two faces of one **electroweak** interaction, split apart by the **Higgs field**. Its potential has no stable centre, so the field settles off-axis and the symmetry breaks. _Figure 005 — The Higgs mechanism: the field rolls into the brim of a Mexican-hat potential, giving the weak bosons mass. _ That single act of symmetry breaking gives the _W_ and _Z_ their mass, hands every fermion a mass through its coupling, and leaves behind a physical **Higgs boson** — found at the LHC in 2012. What makes the theory formidable is not just its scope but its precision: quantities like the electron's magnetic moment agree with experiment to more than ten digits, a level of confirmation no other physical theory matches. The Standard Model is not the end. Neutrino masses, the nature of dark matter, the matter–antimatter asymmetry, and gravity itself all point past it — the open frontier the course closes on. --- ## Contents ### 1. Foundations 1. [From the Electron to the Particle Zoo](/particle-physics/foundations/historical-overview-particle-zoo) 2. [Basic Concepts and Particle Classification](/particle-physics/foundations/particle-physics-basic-concepts) 3. [Fundamental Interactions and Force Carriers](/particle-physics/foundations/fundamental-interactions-force-carriers) ### 2. Units and Kinematics 1. [Natural Units and Scales](/particle-physics/units-kinematics/natural-units-and-scales) 2. [Four-Vectors and Invariant Mass](/particle-physics/units-kinematics/four-vectors-invariant-mass) 3. [Decay, Scattering, and Mandelstam Variables](/particle-physics/units-kinematics/decay-scattering-kinematics-mandelstam) 4. [Cross Sections and the Golden Rule](/particle-physics/units-kinematics/cross-sections-golden-rule) ### 3. Symmetries and Conservation Laws 1. [Conservation Laws and Symmetries](/particle-physics/symmetries/conservation-laws-symmetries) 2. [Discrete Symmetries — C, P, T, and CPT](/particle-physics/symmetries/discrete-symmetries-cpt) 3. [Parity Violation and the Weak Force](/particle-physics/symmetries/parity-violation-weak) 4. [Isospin, SU(2), and Flavor SU(3)](/particle-physics/symmetries/su2-su3-flavor-symmetry) ### 4. The Quark Model 1. [The Eightfold Way and SU(3) Flavor](/particle-physics/quark-model/eightfold-way-su3) 2. [Meson Multiplets and Quantum Numbers](/particle-physics/quark-model/meson-spectroscopy) 3. [Baryon Multiplets, Spin, and the Color Puzzle](/particle-physics/quark-model/baryon-spectroscopy) 4. [Color, Confinement, and Exotic Hadrons](/particle-physics/quark-model/color-confinement-exotics) ### 5. Relativistic Wave Equations 1. [The Klein-Gordon Equation](/particle-physics/relativistic-wave-equations/klein-gordon-equation) 2. [The Dirac Equation and Spinors](/particle-physics/relativistic-wave-equations/dirac-equation-spinors) 3. [Antiparticles and Hole Theory](/particle-physics/relativistic-wave-equations/antiparticles-hole-theory) ### 6. Quantum Electrodynamics 1. [Feynman Rules for QED](/particle-physics/qed/feynman-rules-qed) 2. [Tree-Level QED Processes](/particle-physics/qed/qed-tree-processes) 3. [Renormalization and the Running Coupling](/particle-physics/qed/renormalization-running-coupling) 4. [The Anomalous Magnetic Moment](/particle-physics/qed/electron-g-2) ### 7. The Weak Interaction 1. [The V–A Charged Weak Current](/particle-physics/weak-interaction/va-structure-weak) 2. [The W and Z Bosons](/particle-physics/weak-interaction/w-z-bosons-decays) 3. [Quark Mixing and the CKM Matrix](/particle-physics/weak-interaction/ckm-matrix) 4. [CP Violation in Kaons and B Mesons](/particle-physics/weak-interaction/cp-violation-kaons-b-mesons) ### 8. Quantum Chromodynamics 1. [Color SU(3), Gluons, and the QCD Lagrangian](/particle-physics/qcd/color-su3-gluons) 2. [Asymptotic Freedom and Confinement](/particle-physics/qcd/asymptotic-freedom-confinement) 3. [Deep Inelastic Scattering and the Parton Model](/particle-physics/qcd/deep-inelastic-scattering-partons) 4. [Jets, Hadronization, and Testing QCD](/particle-physics/qcd/jets-hadronization) ### 9. Electroweak Unification and the Higgs 1. [The Electroweak Theory](/particle-physics/electroweak-higgs/electroweak-su2-u1) 2. [Spontaneous Symmetry Breaking](/particle-physics/electroweak-higgs/spontaneous-symmetry-breaking) 3. [The Higgs Mechanism](/particle-physics/electroweak-higgs/higgs-mechanism) 4. [The Higgs Boson](/particle-physics/electroweak-higgs/higgs-boson-discovery) 5. [The Standard Model](/particle-physics/electroweak-higgs/standard-model) ### 10. Neutrino Physics 1. [Neutrino Oscillations](/particle-physics/neutrinos/neutrino-oscillations) 2. [Neutrino Mass and the PMNS Matrix](/particle-physics/neutrinos/neutrino-mass-pmns) 3. [Dirac, Majorana, and Neutrino Experiments](/particle-physics/neutrinos/dirac-majorana-experiments) ### 11. Accelerators and Detectors 1. [Accelerators, Colliders, and Luminosity](/particle-physics/experiment/accelerators-luminosity) 2. [Particle Detectors and Subsystems](/particle-physics/experiment/detectors-subsystems) 3. [From Collisions to Discoveries](/particle-physics/experiment/how-discoveries-are-made) ### 12. Beyond the Standard Model 1. [Beyond the Standard Model](/particle-physics/beyond-standard-model/beyond-standard-model) 2. [Grand Unified Theories and Proton Decay](/particle-physics/beyond-standard-model/grand-unified-theories) 3. [Supersymmetry](/particle-physics/beyond-standard-model/supersymmetry) 4. [The Hierarchy Problem and Naturalness](/particle-physics/beyond-standard-model/hierarchy-problem-naturalness) 5. [Dark Matter and Particle Candidates](/particle-physics/beyond-standard-model/dark-matter-candidates) 6. [Matter-Antimatter Asymmetry and Open Questions](/particle-physics/beyond-standard-model/matter-antimatter-open-questions)