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Concept
Strange quark
Summary
The strange quark or s quark (from its symbol, s) is the third lightest of all quarks, a type of elementary particle. Strange quarks are found in subatomic particles called hadrons. Examples of hadrons containing strange quarks include kaons (_Kaon), strange D mesons (_Strange D), Sigma baryons (_Sigma), and other strange particles.
According to the IUPAP, the symbol s is the official name, while "strange" is to be considered only as a mnemonic. The name sideways has also been used because the s quark has an I_3 value of 0 while the u ("up") and d ("down") quarks have values of +1/2 and −1/2 respectively.
Along with the charm quark, it is part of the second generation of matter. It has an electric charge of −1/3 e and a bare mass of 95MeV/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 (sometimes called antistrange quark or simply antistrange), which differs from it only in that some of its properties have equal magnitude but opposite sign.
The first strange particle (a particle containing a strange quark) was discovered in 1947 (kaons), but the existence of the strange quark itself (and that of the up and down quarks) 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.
In the beginnings of particle physics (first half of the 20th century), hadrons such as protons, neutrons and pions were thought to be elementary particles. However, new hadrons were discovered and the "particle zoo" grew from a few particles in the early 1930s and 1940s to several dozens of them in the 1950s.
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