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Strange quark

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Strange quark
CompositionElementary particle
Interactionsstrong, weak, electromagnetic force, gravity
AntiparticleStrange antiquark (
TheorizedMurray Gell-Mann (1964)
George Zweig (1964)
Discovered1968, SLAC
Decays intoUp quark
Electric charge1/3 e
Color chargeYes
Spin1/2 ħ
Weak isospinLH: −1/2, RH: 0
Weak hyperchargeLH: 1/3, RH: −2/3

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 (
), strange D mesons (
), Sigma baryons (
), 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.[2] The name sideways has also been used because the s quark (but also the other three remaining quarks) has an I3 value of 0 while the u ("up") and d ("down") quarks have values of +1/2 and −1/2 respectively.[3]

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 95+9
.[1] 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. Some particles were much longer lived than others; most particles decayed through the strong interaction and had lifetimes of around 10−23 seconds. When they decayed through the weak interactions, they had lifetimes of around 10−10 seconds. While studying these decays, Murray Gell-Mann (in 1953)[4][5] and Kazuhiko Nishijima (in 1955)[6] developed the concept of strangeness (which Nishijima called eta-charge, after the eta meson (
)) to explain the "strangeness" of the longer-lived particles. The Gell-Mann–Nishijima formula is the result of these efforts to understand strange decays.

Despite their work, the relationships between each particle and the physical basis behind the strangeness property remained unclear. In 1961, Gell-Mann[7] and Yuval Ne'eman[8] independently proposed a hadron classification scheme called the eightfold way, also known as 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[9] and George Zweig[10][11] independently proposed the quark model, which at that time consisted only of the up, down, and strange quarks.[12] 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.[13][14] Deep inelastic scattering experiments indicated that protons had substructure, and that protons made of three more-fundamental particles explained the data (thus confirming the quark model).[15]

At first people were reluctant to identify the three-bodies as quarks, instead preferring Richard Feynman's parton description,[16][17][18] but over time the quark theory became accepted (see November Revolution).[19]

See also[edit]


  1. ^ a b M. Tanabashi et al. (Particle Data Group) (2018). "Review of Particle Physics". Physical Review D. 98 (3): 1–708. Bibcode:2018PhRvD..98c0001T. doi:10.1103/PhysRevD.98.030001. hdl:10044/1/68623. PMID 10020536.
  2. ^ Cohen, Richard E.; Giacomo, Pierre. Symbols, Units, Nomenclature and Fundamental Constants in Physics (PDF) (2010 ed.). IUPAP. p. 12. Archived from the original (PDF) on 18 March 2015. Retrieved 25 March 2017.
  3. ^ McGervey, John D. (1983). Introduction to Modern Physics (second ed.). New York: Academic Press. p. 658. ISBN 978-0-12-483560-3. Retrieved 25 March 2017.
  4. ^ M. Gell-Mann (1953). "Isotopic Spin and New Unstable Particles" (PDF). Physical Review. 92 (3): 833. Bibcode:1953PhRv...92..833G. doi:10.1103/PhysRev.92.833.
  5. ^ Johnson, G. (2000). Strange Beauty: Murray Gell-Mann and the Revolution in Twentieth-Century Physics. Random House. p. 119. ISBN 978-0-679-43764-2. By the end of the summer ... [Gell-Mann] completed his first paper, 'Isotopic Spin and Curious Particles' and send it of to Physical Review. The editors hated the title, so he amended it to 'Strange Particles'. They wouldn't go for that either—never mind that almost everybody used the term—suggesting insteand [sic] 'Isotopic Spin and New Unstable Particles'.
  6. ^ Nishijima, Kazuhiko (1955). "Charge Independence Theory of V Particles". Progress of Theoretical Physics. 13 (3): 285. Bibcode:1955PThPh..13..285N. doi:10.1143/PTP.13.285.
  7. ^ Gell-Mann, Murray (2000) [1964]. "The Eightfold Way: A theory of strong interaction symmetry". In Ne'eman, Y. (ed.). The Eightfold Way. Westview Press. p. 11. ISBN 978-0-7382-0299-0.
    Original: Gell-Mann, Murray (1961). "The Eightfold Way: A theory of strong interaction symmetry". California Institute of Technology. Synchrotron Laboratory Report CTSL-20.
  8. ^ Y. Ne'eman (2000) [1964]. "Derivation of strong interactions from gauge invariance". In M. Gell-Mann, Y. Ne'eman (ed.). The Eightfold Way. Westview Press. ISBN 978-0-7382-0299-0.
    Original Y. Ne'eman (1961). "Derivation of strong interactions from gauge invariance". Nuclear Physics. 26 (2): 222. Bibcode:1961NucPh..26..222N. doi:10.1016/0029-5582(61)90134-1.
  9. ^ Gell-Mann, Murray (1964). "A Schematic Model of Baryons and Mesons". Physics Letters. 8 (3): 214–215. Bibcode:1964PhL.....8..214G. doi:10.1016/S0031-9163(64)92001-3.
  10. ^ Zweig, G. (1964). "An SU(3) Model for Strong Interaction Symmetry and its Breaking". CERN Report No.8181/Th 8419.
  11. ^ Zweig, G. (1964). "An SU(3) Model for Strong Interaction Symmetry and its Breaking: II". CERN Report No.8419/Th 8412.
  12. ^ Carithers, B.; Grannis, P. (1995). "Discovery of the Top Quark" (PDF). Beam Line. 25 (3): 4–16. Retrieved 2008-09-23.
  13. ^ Bloom, E. D.; Coward, D.; et al. (1969). "High-Energy Inelastic ep Scattering at 6° and 10°". Physical Review Letters. 23 (16): 930–934. Bibcode:1969PhRvL..23..930B. doi:10.1103/PhysRevLett.23.930.
  14. ^ Breidenbach, M.; Friedman, J.; et al. (1969). "Observed Behavior of Highly Inelastic Electron–Proton Scattering". Physical Review Letters. 23 (16): 935–939. Bibcode:1969PhRvL..23..935B. doi:10.1103/PhysRevLett.23.935. OSTI 1444731. S2CID 2575595.
  15. ^ Friedman, J. I. "The Road to the Nobel Prize". Hue University. Archived from the original on 25 December 2008. Retrieved 29 September 2008.
  16. ^ Feynman, R. P. (1969). "Very High-Energy Collisions of Hadrons" (PDF). Physical Review Letters. 23 (24): 1415–1417. Bibcode:1969PhRvL..23.1415F. doi:10.1103/PhysRevLett.23.1415.
  17. ^ Kretzer, S.; Lai, H.; et al. (2004). "CTEQ6 Parton Distributions with Heavy Quark Mass Effects". Physical Review D. 69 (11): 114005. arXiv:hep-th/0307022. Bibcode:2004PhRvD..69k4005K. doi:10.1103/PhysRevD.69.114005. S2CID 119379329.
  18. ^ Griffiths, D. J. (1987). Introduction to Elementary Particles. John Wiley & Sons. p. 42. ISBN 978-0-471-60386-3.
  19. ^ Peskin, M. E.; Schroeder, D. V. (1995). An introduction to quantum field theory. Addison–Wesley. p. 556. ISBN 978-0-201-50397-5.

Further reading[edit]