fundamental particles

• Elementary particles


  Particles that are the fundamental constituents of matter
• Classification of elementary particles

  1. Quarks and strangeness

  2. Forces of nature and messenger particles

  
• General properties of elementary particles


  • Advent of high energy particle colliders has allowed the observation of new particles
  • Many particles are short lived and their existence can only be inferred from results of decay processes and not by direct observation
  • Particles are categorised through the standard model

  
• Groupings of known particles


  • Fermions or bosons
  • Leptons or hadrons
  • Particle or antiparticle

  
• Forces of nature


  • Strong
  • Electromagnetic
  • Weak
  • Gravity
• Electro-weak force


  Unification of electromagnetic and weak forces
• Attempts are being made to devise theories that unify the strong force with the electro-weak force: GRAND UNIFIED THEORY (GUT)
• Fermion


  Particle with intrinsic angular momentum or spin of 1/2, 3/2, 5/2, etc.
• Boson


  Particle with spin of 0, 1, 2, etc.
• Fermions


  • Obey the Pauli exclusion principle - only a single fermion can be assigned to a given quantum state
• Bosons


  • Do not obey the Pauli exclusion principle - many bosons can be placed in the same quantum state
• Hadron


  Particle that experiences the strong force
• Lepton


  Particle that experiences only the weak force and the electromagnetic force
• Meson


  Hadron that is a boson
• Baryon


  Hadron that is a fermion
• Particle


  Has the same mass and spin but opposite charge, if charged, and the opposite sign of quantum numbers such as strangeness

  
• Particles and antiparticles will annihilate which results in the release of energy in the form of other particles or photons
• Lepton families


  • 3 families of leptons
• Lepton number


  Quantum number for leptons, +1 for a particle and -1 for an antiparticle

  
• In any reaction lepton number is conserved

  
• Baryon number


  Quantum number for baryons, +1 for a baryon and -1 for an antibaryon, 0 for other particles

  
• In any reaction baryon number is conserved and a process that changes the net baryon number cannot occur
• Strangeness


  Quantum number associated with hadrons, conserved in interactions involving the strong force

  
• The idea of strangeness allows the grouping of baryons and mesons in a pattern known as The Eightfold Way
• Looking at patterns for other forms of baryon and meson spin > 1/2 or spin > 0 allowed the prediction of other massive particles

  
• Quark


  Sub-unit that mesons and baryons are built from, has charge which is a multiple ±1/3, baryon number which is a multiple ±1/3, and strangeness of either 0 or -1

  
• Combinations of quarks in groups of 3 result in the predicted properties for the baryons. Mesons are quark-anti-quark pairs.

  
• Messenger particles


  Field particles or exchange particles that mediate the four fundamental forces
• Messenger particles for the four fundamental forces


  • Virtual photons for electromagnetic
  • Pions and gluons for strong
  • W+, W-, Z0 particles for weak
  • Gravitons for gravitational
• All of the above messenger particles have been detected with the exception of gravitons
• Properties of the four fundamental forces


  • Relative strength
  • Range of force
  • Mediating particle
  • Mass (GeV/c2)
• Gravity


  Universal attractive force, decreases with distance, increases with mass, weak force
• Electromagnetism


  Charge based force, like charges repel, unlike charges attract, force decreases with distance, important for holding matter together
• Colour (strong) force


  Force that only involves quarks, at very short range 10-15 m, force increases with distance
• Weak force


  Changes the flavour of quarks, responsible for radioactive decay
• The Standard Model of Particle Physics is a theory that describes the fundamental particles and forces of nature