• All particles of?matter?are made up of either?quarks?and/or?leptons
  • The?standard?model?of particle physics categorises quarks and leptons by charge and mass

Quarks and leptons form the standard model of particle physics. The first generation of particles make up all ordinary matter

• Hadrons?are made up of?quarks?and interact with the?strong nuclear force
• Baryons?and?mesons?are types of hadron
  • Baryons?consist of?3 quarks
  • Mesons?consist of a?quark-antiquark pair

   

• The most common baryons are protons and neutrons
• The most common mesons are pions and kaons

Hadrons may be either a baryon or a meson. Both baryons and mesons interact with the strong nuclear force

Anti-hadrons may be either an anti-baryon or an anti-meson

• Quarks have never been discovered on their own, always in pairs or groups of three
• Note that all baryons or mesons have integer (whole number) charges eg. +1e, -2e etc.
• This means quarks in a baryon are either all quarks or all anti–quarks. Combination of quarks and anti–quarks don’t exist in a baryon
  • e.g. 

    

   

• The anti–particle of a meson is still a quark and anti–quark pair. The difference being the quark becomes the anti–quark and vice versa

Leptons

• Leptons?are a group of?fundamental?(elementary) particles
  • This means they are not made up of any other particles (no quarks)

   

• Leptons interact with other particles via the?weak,?electromagnetic?or?gravitational?interactions
  • Unlike hadrons (baryons & mesons), leptons?do?not?interact via the strong nuclear force

   

• The most common leptons are:
  • The electron, e–
  • The electron neutrino, ve
  • The muon, μ–
  • The muon neutrino, vμ

   

The most common leptons are the electron and muon, along with their associated neutrinos

• The muon is similar to the electron but is slightly?heavier
• Electrons and muons?both?have a charge of -1e?and a mass of 0.0005u
• Neutrinos are the most abundant leptons in the universe and have?no charge?and?negligible?mass (almost 0)
• Although quarks are fundamental particles too, they are not classed as leptons

Photons

• Photons are a group of particles which mediate the?electromagnetic interaction
  • They are?uncharged
  • They have zero?mass

• They are sometimes called "exchange bosons" because they mediate one of the fundamental forces (electromagnetism)
  • For example, the electrostatic repulsion between two electrons is understood in terms of?exchanging photons