Discovering Particles

Feynman diagrams

Matter particles interact with one another by emitting and absorbing force carriers. When two particles are smashed together at high speeds, their interaction can result in energy being released for the creation of new leptons or hadrons. The muon and tau leptons, and all hadrons except the proton and neutron, survive for only a fraction of a second before they decay. This is a process through which the initial particle is replaced by two or more particles of lower mass.

Particle interactions and decays are represented pictorially in Feynman diagrams, named after their inventor, Richard Feynman. These diagrams show notionally development in time from left to right, and show positions in space vertically. Different types of line are used to identify different types of particle. Points where lines meet are called vertices.

Feynman diagrams are powerful calculational tools. Individual lines and vertices are shorthand for lengthy mathematical expressions. Multiplying together the expressions for all lines and vertices of a diagram for a given interaction or decay gives a measure of how often the process occurs.

Some classes of Feynman diagram have been given names based on their appearance, making it easier for physicists to refer to them when discussing calculations. Examples include tree diagrams, tadpole diagrams, loop diagrams, box diagrams and penguin diagrams.

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