Investigate the Standard Model of matter

The standard model:

The standard model is a theory describing three of the four fundamental forces (electromagnetic, strong and weak), and classifying all known elementary particles.

The elementary particles in standard model are either Fermions or Bosons.

Fermions are particles which obey the fermi-dirac statistics. Fermions obey Pauli’s exclusion principle. These are further classified into Quarks and Leptons.

Bosons are particles which obey the bose-einstein statistics. These particles do not obey Pauli’s exclusion principle.


Quarks are elementary particles which form neutrons and protons.

  • In the 1960s it was discovered that protons and neutrons were made of more fundamental particles.
  • Particles like neutrons and protons are called Hadrons. Hadrons are all the particles which are made up of quarks.
  • To understand the fundamental particles that constituted protons, neutrons and other hadrons, Murray Gell-Mann and George Zweig, based on the various experiments conducted till then, proposed a model where all Hadrons were made up of only three quarks. These three Quarks were called up, down and strange.
  • Later three more types of quarks were added in the model, and they were called charm, bottom and top.
  • All the six quarks have very different masses .
  • They either posses or charge  (-1 denotes charge of an electron)
  • The charge on a Hadron is the sum of charges of its constituting quarks.
    • There are two kind of Hadrons : Baryons are particles which are made up of three quarks, while mesons are made of two quarks.
  • Just like electric charges are binary and come in positive or negative, quarks can have three different charges.
    • Quarks can have red, green or blue charge.
  • Each quark has its own antiparticle.


  • Leptons are another class of fundamental
  • These class of particles are some of the lightest .
  • There are three different kinds of leptons :
    • electrons (e)
    • tautau
    • muonsmuon
    • electron neutrinoselectron neutrino
    • muon neutrinostau neutrino
    • tau neutrinosmuon neutrino
  • The neutrinos are electrically chargeless , while electrons , tau and muons are negatively charged.
  • Each of the electrons have their own antiparticles.

Fundamental forces:

  • According to standard model, the fundamental forces can be understood using Quantum mechanics, which suggests that force between particles can be explained in terms of exchange of special force carrying particles called gauge bosons.
  • Bosons are particles which obey the fermi-dirac statistics. Bosons do not obey Pauli exclusion principle.
  • The standard model includes explanation for three of the four fundamental forces with Boson particles.
    • The strong nuclear force is mediated by gluons.
      • Gluons hold quarks together to form Hadrons
      • There are eight different kinds of gluons.
    • The weak force is mediated by W and Z particles.
      • The W particles can have positive or negative charge.
      • The Z particle is electrically neutral.
    • The electromagnetic force is mediated by photons.
  • The hypothetical particle graviton, which is required for gravitational force to be explained as exchange of force, has not yet been directly observed. Hence gravitational force is yet not included in standard model.

Extract from Physics Stage 6 Syllabus © 2017 NSW Education Standards Authority (NESA)