The Standard Model

Elementary Particles

• Elementary particles are the smallest known building blocks of the universe, with no internal structure and considered zero-dimensional points.
• Types of elementary particles included are fundamental fermions (matter and antimatter) and bosons (mediators of forces).
• Composite particles contain two or more elementary particles.

Matter and Antimatter

• Each matter particle has a corresponding antimatter particle, denoted with a line above its symbol.
• Matter and antimatter particles share the same mass but have opposite electric charges and quantum numbers.
• When a matter particle collides with its antimatter counterpart, they annihilate, producing other subatomic particles.

Standard Model

• The Standard Model is the mathematical framework that describes elementary particles and their interactions.
• Quantum numbers guide the classification of particles, including charge, spin, baryon number, and color charge.
• Example: A proton has a charge of +1e consisting of two up quarks and one down quark.

Fermions

• There are 12 fermions in the Standard Model, categorized into quarks and leptons.
• Six flavors of quarks: up, down, charm, strange, top, and bottom; their charges are either +2/3e or -1/3e.
• Hadrons, made of quarks, are categorized as baryons (3 quarks) or mesons (2 quarks).

Color Charge

• Color charge is essential for forming stable combinations of quarks, assigned as red, green, and blue (and corresponding anti-colors).
• Baryons require combinations that yield a color-neutral (white) status, with protons and neutrons as common examples.
• Quarks carry a baryon number of +1/3, while anti-quarks have -1/3, ensuring overall baryon number conservation.

Leptons

• Unlike quarks, leptons exist independently and interact via weak nuclear force.
• Common leptons include the electron, muon, and tau, each with a corresponding neutrino.
• Example of interaction: Beta-minus decay involves the emission of an electron and anti-neutrino.

Fundamental Forces and Gauge Bosons

• Four fundamental forces govern interactions: strong, electromagnetic, weak, and gravitational.
• Gauge bosons are mediators for these forces:
  • Gluon: mediates the strong nuclear force.
  • Photon: carries the electromagnetic force.
  • Z and W bosons: mediate weak nuclear force.
• The graviton is a theoretical particle proposed for gravitational interactions.

Conservation Laws

• Conservation of mass-energy and momentum is vital; annihilation produces energy based on E=mc².
• Charge conservation dictates that the total charge before and after interactions must remain equal.
• Baryon and lepton number conservation is essential during particle interactions to avoid discrepancies.

Neutron Decay Example

• Neutron decays to a proton demonstrating conservation laws:
  • Mass-energy: 939.57 → 938.27 + 0.511 + 0 + 0.779
  • Charge: 0e → 1e + -1e + 0 + 0
  • Baryon number: 1 → 1 + 0 + 0 + 0
  • Lepton number: 0 → 0 + 1 + -1 + 0

Symmetries in Physics

• Charge reversal: interactions hold when all particles are replaced with their antiparticles.
• Parity symmetry: laws of physics remain unchanged if particle movements are inverted.
• Time reversal: interactions can occur in reverse without violating physical laws.

CPT Symmetry

• CPT (Charge, Parity, Time) symmetry implies a mirror-image universe follows the same physical laws as our own.

Supersymmetry

• Supersymmetry extends the Standard Model, predicting partner particles for every Standard Model particle.
• Addresses limitations in the Standard Model, particularly regarding the Higgs boson mass.