The standard model was developed in the 1970s and it classifies all of the known elementary particles, of which there are 17. Twelve of these are matter particles, grouped as quarks and leptons. Another four make up the charge carriers group, one for each of the fundamental forces. The final elementary particle and the latest addition to the standard model is the Higg’s Boson.
By definition, quarks are a group of subatomic particles carrying a fractional charge, which join to form hadrons. Quarks can never be found alone, only ever in groups of other quarks or antiquarks (the reason for this is explained by quantum chromodynamics).
The two most commonly occurring quarks in nature are the up and down quark, making up protons and neutrons.
Because the up quark has a charge of +2/3 and the down quark a charge of -1/3, the proton will have an overall charge of 1 and a neutron the overall charge of 0.
The quarks are separated into three generations of increasing mass, with the up and down quark first generation quarks. As they have the lowest mass, they are the most stable and higher generation quarks are not observed in nature and quickly decay into first generation quarks.
There are six leptons, these are either electrons or neutrinos, they are different to quarks in that they do not feel the strong force. Leptons are split into two groups – charged (electron-like) and uncharged (neutrinos).
Charged leptons consist of electrons, muon and tau – with electron being the first generation particle and therefore most common. Muon and tau will quickly decay to electrons and are only produced in very high energy collisions. Electrons are found within all atoms but, because they do not feel the strong force, they are in shells outside of the nucleus.
Neutrinos rarely interact with other particles and are therefore very difficult to detect.
The force carriers, also known as gauge bosons, are the photon, gluon, z boson and w boson. Three of the fundamental forces: electromagnetic, strong and weak, are produced by the exchange of these force carrying bosons.
The strong force has the gluon, the electromagnetic force has the photon and the weak force has the z and w bosons. The gravitational force should have the graviton as its boson, however it has not yet been found or confirmed.
The Higgs boson was predicted in the 1960s by Peter Higgs but wasn’t found until 2012, at CERN. Although even this hasn’t been confirmed as the Higg’s particle but is instead a particle which seems to meet the predictions of the properties of the Higgs Boson.
The Higg’s boson is an unstable particle associated with the Higgs field, essentially responsible for giving all particles a mass. It is the first scalar elementary particle to be discovered.