Subatomic Particles

Subatomic Particles is the eighteenth and final lecture within the Properties of Matter subtopic of PH1011. It covers a brief introduction of particle physics, in particular examples of sub-atomic particles, their basic properties and how they can be produced.

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The Standard Model
According to the standard model, several classes of subatomic particle exist:
 * 6 quarks
 * 6 leptons
 * Force carriers (eg the photon, the gluon)
 * The Higgs Boson
 * Antiparticles

These particles make up the greater subatomic particles (eg a neutron is made of three quarks; it is a baryon, which is a subset of hadrons).

Mass and Energy
The mass of a proton is 1.67262158 x10-27kg. The number of digits on this value make it difficult to work with, so the unit of mass must be broken down into something with greater versitility. As E = mc2, mass can be given as J/c2 or MeV/c2. In these units a proton is 938 MeV/c2, and an electron (for comparison) is 0.511 MeV/c2.

Properties
The most important properties of these particles are their masses, charges, lifetimes and spins (eg electron spin; see chemistry).

Spin is a property of angular momentum, and can have a value of a positive integer or half value given by Sz = ms(h/2π), m being the magnetic spin quantum number (s = 1, s-1,... -s) and s being the spin quantum number. Particles with integer spin (eg photons, pions) are bosons and particles with half integer spins are fermions (eg electrons, protons). Fermions obey the Pauli exclusion principle where bosons do not. Particles which experience the strong force are defined as hadrons (eg protons, neutrons), whereas particles which do not are leptons (eg electrons, neutrinos). Hadron/bosons are mesons (eg pion, kaon) and hadron/fermions are baryons (eg protons).

Antiparticles
An antiparticle is a (mostly theoretical) complimentary particle which exists in relation to a matter particle; it is identical but for having an opposite charge. An example of this is the positron - an electron by all means except for its positive charge. Interaction of articles with antiparticles causes destruction of them both, and production of high energy protons.

Summary
Matter exists at absolutely tiny levels, in various forms. The masses of these can be expressed in MeV/c2 as well as in grams. Their defining properties are their mass, charge, life and spins, and all particles have anti-matter equivalents - the same particle with opposite charge.