Eightfold way

In physics, the Eightfold Way is a term coined by American physicist Murray Gell-Mann for a theory organizing subatomic baryons and mesons into octets (alluding to the Noble Eightfold Path of Buddhism). The theory was independently proposed by Israeli physicist Yuval Ne'eman and led to the subsequent development of the quark model.

The meson octet. Particles along the same horizontal line share the same strangeness, s, while those on the same diagonals share the same charge, q.

In addition to organizing the mesons and spin-1/2 baryons into octets, the principles of the Eightfold Way also applied to the spin-3/2 baryons, forming a decuplet. However, one of the particles of this decuplet had never been previously observed. Gell-Mann called this particle the Ω⁻ and predicted in 1962 that it would have a strangeness −3, electric charge −1 and a mass near 1,680 MeV/c². In 1964 a particle closely matching these predictions was discovered by a particle accelerator group at Brookhaven, making the Eightfold Way a triumphant success. Gell-Mann went on to receive the 1969 Nobel Prize in physics for his work on the theory of elementary particles.

The baryon decuplet

The baryon octet

The Eightfold Way may be understood in modern terms as a consequence of flavor symmetries between various kinds of quarks. Since the strong nuclear force is the same for quarks of any flavor, replacing one flavor of quark with another in a hadron should not alter its mass very much. Mathematically, this replacement may be described by elements of the group SU(3). The octets and other arrangements are representations of this group; for a more detailed explanation of this fact, see the article Particle physics and representation theory.

References

• Griffiths, David (1987). Introduction to Elementary Particles. New York: John Wiley & Sons. ISBN 0-471-60386-4.