6.8.2 Hadrons & Leptons

Subatomic Particles

• Subatomic particles can be divided into two families:
  • Hadrons
  • Leptons

Hadrons

• Hadrons are affected by the strong nuclear force
• They are made of quarks
• Include:
  • Protons
  • Neutrons
  • Mesons
  • and their corresponding antiparticles
• If charged they experience the electromagnetic force
• Decay occurs by the weak nuclear force

• The large hadron collider at CERN (LHC) is used to look inside fundamental particles

Leptons

• Are fundamental particles
  • Fundamental particles have no internal structure
  • They cannot be divided or split into smaller parts
  • This is because they are not composed of quarks
• Leptons are not affected by the strong nuclear force 
• There are 6 leptons that include:
  • Electrons
  • Neutrinos
  • Muons
• If charged they experience the electromagnetic force

 

The six leptons are all fundamental particles

• The muon and tau particle are very similar to the electron but with slightly larger mass
• Electrons, muon and tau particles all have a charge of −1e and a mass of 0.0005u
  • u is the unified atomic mass unit
  • It has the value 1.661 × 10⁻²⁷ kg
• There are three flavours (types) of neutrinos
  • The electron neutrino, ν_e
  • The muon neutrino, ν_μ
  • The tau neutrino, ν_τ
• Neutrinos are the most abundant leptons in the universe
  • They have no charge and negligible mass (almost 0)
• Neutrinos are produced in particle interactions which also involve the other leptons
  • For example, if an electron is produced in a particle interaction, an electron neutrino will also be produced
• Leptons interact through the weak interaction, electromagnetic force and gravitational forces
• However, they do not interact with the strong force
  • Although quarks are fundamental particles too, they are not classed as leptons
  • Leptons do not interact with the strong force, whilst quarks do