Down quark

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Down quark
ħ
Weak isospinLH: −1/2, RH: 0
Weak hyperchargeLH: +1/3, RH: −2/3

The down quark (symbol: d) is a type of

hadrons. Down quarks are most commonly found in atomic nuclei, where it combines with up quarks to form protons and neutrons
. The proton is made of one down quark with two up quarks, and the neutron is made up of two down quarks with one up quark. Because they are found in every single known atom, down quarks are present in all everyday matter that we interact with.

The down quark is part of the

gravitation, electromagnetism, weak interactions, and strong interactions. The antiparticle of the down quark is the down antiquark (sometimes called antidown quark or simply antidown), which differs from it only in that some of its properties have equal magnitude but opposite sign
.

Its existence (along with that of the up and

Stanford Linear Accelerator Center
in 1968.

History

Murray Gell-Mann
George Zweig

In the beginnings of particle physics (first half of the 20th century),

flavor symmetry
.

This classification scheme organized the hadrons into

Stanford Linear Accelerator Center.[8][9] 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).[10]

At first people were reluctant to identify the three-bodies as quarks, instead preferring

November Revolution).[14]

Mass

Despite being extremely common, the bare mass of the down quark is not well determined, but probably lies between 4.5 and 5.3 MeV/c2.[15] Lattice QCD calculations give a more precise value: 4.79±0.16 MeV/c2.[16]

When found in mesons (particles made of one quark and one antiquark) or baryons (particles made of three quarks), the 'effective mass' (or 'dressed' mass) of quarks becomes greater because of the binding energy caused by the gluon field between quarks (see mass–energy equivalence). For example, the effective mass of down quarks in a proton is around 300 MeV/c2. Because the bare mass of down quarks is so small, it cannot be straightforwardly calculated because relativistic effects have to be taken into account,

References

  1. ^ a b M. Tanabashi et al. (Particle Data Group) (2018). "Review of Particle Physics". Physical Review D. 98 (3): 1–708.
    PMID 10020536
    .
  2. ^ M. Gell-Mann (2000) [1964]. "The Eightfold Way: A theory of strong interaction symmetry". In M. Gell-Mann, Y. Ne'eman (ed.). The Eightfold Way.
    ISBN 978-0-7382-0299-0.
    Original: M. Gell-Mann (1961). "The Eightfold Way: A theory of strong interaction symmetry". Synchrotron Laboratory Report CTSL-20. California Institute of Technology
    .
  3. ^ Y. Ne'eman (2000) [1964]. "Derivation of strong interactions from gauge invariance". In M. Gell-Mann, Y. Ne'eman (ed.). The Eightfold Way.
    doi:10.1016/0029-5582(61)90134-1
    .
  4. ^ M. Gell-Mann (1964). "A Schematic Model of Baryons and Mesons".
    doi:10.1016/S0031-9163(64)92001-3
    .
  5. ^ G. Zweig (1964). "An SU(3) Model for Strong Interaction Symmetry and its Breaking". CERN Report No.8181/Th 8419.
  6. ^ G. Zweig (1964). "An SU(3) Model for Strong Interaction Symmetry and its Breaking: II". CERN Report No.8419/Th 8412.
  7. ^ B. Carithers, P. Grannis (1995). "Discovery of the Top Quark" (PDF). Beam Line. 25 (3): 4–16. Retrieved 2008-09-23.
  8. ^ E. D. Bloom; et al. (1969). "High-Energy Inelastic e–p Scattering at 6° and 10°".
    doi:10.1103/PhysRevLett.23.930
    .
  9. ^ M. Breidenbach; et al. (1969). "Observed Behavior of Highly Inelastic Electron–Proton Scattering" (PDF).
    S2CID 2575595
    .
  10. ^ J. I. Friedman. "The Road to the Nobel Prize".
    Hue University. Archived from the original
    on 2008-12-25. Retrieved 2008-09-29.
  11. ^ R. P. Feynman (1969). "Very High-Energy Collisions of Hadrons" (PDF).
    doi:10.1103/PhysRevLett.23.1415
    .
  12. ^ S. Kretzer; H. Lai; F. Olness; W. Tung (2004). "CTEQ6 Parton Distributions with Heavy Quark Mass Effects".
    S2CID 119379329
    .
  13. ^ D. J. Griffiths (1987). Introduction to Elementary Particles.
    ISBN 978-0-471-60386-3
    .
  14. ^ M. E. Peskin, D. V. Schroeder (1995). An introduction to quantum field theory.
    ISBN 978-0-201-50397-5
    .
  15. ^ J. Beringer; et al. (Particle Data Group) (2013). "PDGLive Particle Summary 'Quarks (u, d, s, c, b, t, b′, t′, Free)'" (PDF). Particle Data Group. Retrieved 2013-07-23.
  16. ^ Cho, Adrian (April 2010). "Mass of the Common Quark Finally Nailed Down". Science Magazine. Archived from the original on 2012-03-06.

Further reading

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