Strong interaction

__NOTOC__ The strong interaction or strong force is today understood to represent the interactions between quarks and gluons as detailed by the theory of quantum chromodynamics (QCD). The strong force is the fundamental force mediated by gluons, acting upon quarks, antiquarks, and the gluons themselves.

Although the strong force only acts upon elementary particles directly, the force is only observed interacting with hadrons as the nuclear force. As has been shown by many failed free quark searches, the elementary particles affected are unobservable directly. This phenomenon is called confinement, a theory which allows only hadrons to be seen.

History

Before the 1970s, when protons and neutrons were thought to be fundamental particles, the phrase "strong force" was what is today known as the nuclear force or the residual strong force. What were being observed were the "residual" effects of the strong force, which act on hadrons, both baryons and mesons. This force was postulated to overcome the electric repulsion between protons in the nucleus, and for its strength (at short distances) it was dubbed the "strong force". After the discovery of quarks, scientists realized that the force was actually acting upon the quarks and gluons making up the protons, not the protons themselves. For some time after this realization, the older notion was referred to as the residual strong force, and the "new" strong interaction was called colour force.

Details

Quantum chromodynamics, a part of the standard model of particle physics, is a typical non-Abelian gauge theory based on a local (gauge) symmetry group called SU(3). All the particles in this theory interact with each other, through the strong force. The strength of the interaction is parametrized by the strong coupling constant. This strength is, as usual, modified by the gauge colour charge of the particle. This really refers to a group theoretical property whose meaning is explained in the article on colour charge. Quarks and gluons are the only fundamental particles which carry non-vanishing colour charge, and hence participate in the strong interactions.

References

Introduction to Elementary Particles, by David J. Griffiths (New York: John Wiley & Sons, 1987) ISBN 0471603864

The Last Sorcerers: The Path from Alchemy to the Periodic Table, by Richard Morris (Washington, DC: Joseph Henry Press, 2003) ISBN 0309505933

External links

MISN-0-280: The Strong Interaction (PDF file) by J.R. Christman for Project PHYSNET.

Quantum chromodynamics | Particle physics | Nuclear physics

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