Introduction - Elementary Particles

What is the world made from? What are the building blocks of the universe? Answer: There are 2 types of elementary particle - Fundamental Bosons (responsible for force and mass) & Fundamental Fermions (Quarks & Leptons).

Any other particles are composed of multiple elementary particles - and such composite particles are called Hadrons. Again, there are 2 types of Hadron - Composite Bosons (Mesons) and Composite Fermions (Baryons).

The over-arching principle is that particles (elementary and composite) are divided into 2 categories - Bosons and Fermions. Bosons are somewhat ethereal concepts - they aren't actually matter itself but responsible for the interactions between matter particles. So the real building blocks of the universe are Fermions - Quarks and Leptons which when combined create protons, neutrons and thus atoms, molecules and everything that makes up real stuff - animals, vegetables and minerals.

Bosons

Formal definition of a boson = particles conforming to Bose-Einstein Statistics

Fundamental Bosons (elementary particles)

• Photons - transmit light and other electromagnetic energy
• Gluons - responsible for the Strong force that holds Quarks together in a Hadron
• W & Z Bosons - responsible for the Weak force
• Graviton (theoretical only) - responsible for Gravity
• Higgs Boson - responsible for mass in particles that have mass

Composite Bosons - Mesons

Mesons are composed of 1 Quarks and 1 anti-Quark. There are literally dozens of them; too many to list here but well known ones include:

• Positive Pion
• Negative Pion
• Neutral Pion
• Kaon (of which there are 4 types)

Fermions

Formal definition of a fermion = particles conforming to Fermi-Dirac Statistics

Fundamental Fermions - Quarks & Leptons

• All Quarks. There are 6 types (flavours) of Quark (+ 6 anti-quarks), 4 of which immediately decay into Up or Down Quarks which are the only stable quarks:
  • Up
  • Down
  • Strange
  • Charm
  • Bottom
  • Top
• All Leptons
  • Charged Leptons
    • Electron
    • Muon
    • Tau
  • Neutral Leptons
    • Electron Neutrino
    • Muon Neutrino
    • Tau Neutrino

Composite Fermions - Baryons

Baryons are made from 3 Quarks e.g.

• Proton
• Neutron
• Various exotic baryons composed of Strange, Charm or Bottom quarks have been briefly observed