Classification of Particles

There are very many subatomic particles, and over time they have been sorted into classes based on their properties. There are six classes of particle: leptons, hadrons, baryons, mesons, bosons and fermions. The classes are not separated, so an individual particle may be in two classes simultaneously. For example, a proton is both a baryon and a hadron (all mesons and baryons are also hadrons). The properties of the classes are summarised below.

Leptons – e.g. electron, neutrino. Leptons do not interact via the strong interaction. There are six leptons in total - three charged leptons called the electron, muon and tau, and their associated neutrinos, the neutrino, muon nuetrino and tau neutrino respectively.

Hadrons – e.g. neutrons and protons. Particles that interact by the strong interaction are called hadrons, so baryons and mesons are also hadrons. Hadrons also experience the weak force. They composed of quarks, either as quark-antiquark pairs (mesons) or as three quarks (baryons).

Baryons – e.g. neutrons and protons, lambda, sigma, xi, and omega particles . Baryons are heavy particles made up of three quarks, as opposed to mesons, made up of two quarks. Baryons are fermions (having half integral spin), while the mesons are bosons (having integral spin).

Mesons - Mesons are intermediate mass particles which are made up of a quark - antiquark pair. Mesons are bosons, carrying forces between particles.

Bosons - Bosons have integer spin. The fundamental forces of nature are mediated by bosons.

Fermions - Fermions have half-integer spin. There are 12 types of elementary fermions: six quarks and six leptons. These are matter particles, as opposed to bosons which carry the fundamental forces between particles.

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