Parton (physics)

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In particle physics of the late 1960s, the partons were hypothetical elementary particles that represented the constituents of the hadron in the “parton model” of strong interaction . The name goes back to the physicist Richard Feynman . In the 1970s, the theory of quantum chromodynamics (QCD) showed that hadrons consist of the quarks postulated by Murray Gell-Mann - Feynman was outvoted in the naming, now one speaks of quarks and gluons as components of a hadron.

The QCD describes the interaction in nuclei in more detail than the parton model. The latter is still used today to describe certain aspects of the interactions at very small distances.

Parton distribution functions

The CTEQ6 PDFs in the MS renormalization scheme at Q  = 2 GeV for gluons (red), up (green), down (blue) and strange quarks (violet). The product of the longitudinal momentum component x and the distribution function f versus x is plotted .

The parton distribution functions (PDF) indicate the probability of finding a particle with a certain longitudinal momentum component x and momentum transfer Q 2 in a hadron. The Parton distribution functions cannot be determined theoretically due to non-perturbative effects of QCD . The known parton distribution functions therefore (and because of the limitations of the lattice scale theory ) come from experimental data.

There are several distribution functions identified by different groups around the world. The most important are:

  • CTEQ , from the CTEQ collaboration
  • GRV , by M. Glück, E. Reya and A. Vogt
  • MRST , by AD Martin, RG Roberts, WJ Stirling, and RS Thorne

literature

  • CTEQ Collaboration, S. Kretzer et al .: CTEQ6 Parton Distributions with Heavy Quark Mass Effects . In: Phys. Rev. , D69, 2004, p. 114005, arxiv : hep-ph / 0307022
  • M. Glück, E. Reya, A. Vogt: Dynamical Parton Distributions Revisited . In: Eur. Phys. J. , C5, 1998, pp. 461-470, arxiv : hep-ph / 9806404
  • AD Martin et al .: Parton distributions incorporating QED contributions . In: Eur. Phys. J. , C39, 2005, pp. 155-161, arxiv : hep-ph / 0411040

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