The strange quark or s quark is the third-lightest of all quarks, a type of elementary particle.
Strange quarks are found in subatomic particles called hadrons. Example of hadrons containing
strange quarks include kaons, strange D mesons (D
s), Sigma baryons, and other strange particles. Along with the charm quark, it is part of
the second generation of matter, and has an electric charge of −1⁄3 e and a bare
mass of 95+5 −5 MeV/c2. Like all quarks, the strange
quark is an elementary fermion with spin-1⁄2, and experiences all four fundamental interactions:
gravitation, electromagnetism, weak interactions, and strong interactions. The antiparticle
of the strange quark is the strange antiquark, which differs from it only in that some of
its properties have equal magnitude but opposite sign.
The first strange particle was discovered in 1947, but the existence of the strange
quark itself was only postulated in 1964 by Murray Gell-Mann and George Zweig to explain
the Eightfold Way classification scheme of hadrons. The first evidence for the existence
of quarks came in 1968, in deep inelastic scattering experiments at the Stanford Linear
Accelerator Center. These experiments confirmed the existence of up and down quarks, and by
extension, strange quarks, as they were required to explain the Eightfold Way.
History In the beginnings of particle physics, hadrons
such as protons, neutron and pions were thought to be elementary particles. However, new hadrons
were discovered, the 'particle zoo' grew from a few particles in the early 1930s and 1940s
to several dozens of them in the 1950s. However some particles were much longer lived than
others; most particles decayed through the strong interaction and had lifetimes of around
10−23 seconds. But when they decayed through the weak interactions, they had lifetimes
of around 10−10 seconds to decay. While studying these decays Murray Gell-Mann and
Kazuhiko Nishijima developed the concept of strangeness) which explained the 'strangeness'
of the longer-lived particles. The Gell-Mann–Nishijima formula is the result of these efforts to
understand strange decays. However, the relationships between each particles
and the physical basis behind the strangeness property was still unclear. In 1961, Gell-Mann
and Yuval Ne'eman proposed a hadron classification scheme called the Eightfold Way, or in more
technical terms, SU(3) flavor symmetry. This ordered hadrons into isospin multiplets. The
physical basis behind both isospin and strangeness was only explained in 1964, when Gell-Mann
and George Zweig proposed the quark model, then consisting only of up, down, and strange
quarks. Up and down quarks were the carriers of isospin, while the strange quark carried
strangeness. While the quark model explained the Eightfold Way, no direct evidence of the
existence of quarks was found until 1968 at the Stanford Linear Accelerator Center. Deep
inelastic scattering experiments indicated that protons had substructure, and that protons
made of three more-fundamental particles explained the data.
At first people were reluctant to identify the three-bodies as quarks, instead preferring
Richard Feynman's parton description, but over time the quark theory became accepted.
See also Quark model
Strange matter Strangeness production
Strangelet Strange star
References
Further reading R. Nave. "Quarks". HyperPhysics. Georgia State
University, Department of Physics and Astronomy. Retrieved 2008-06-29.
A. Pickering. Constructing Quarks. University of Chicago Press. pp. 114–125. ISBN 0-226-66799-5.