# Why Believe in QCD?

## Abstract

I will divide the evidence for QCD into *a priori* evidence and *a posteriori* evidence, obtained by comparing specific QCD predictions with data.^{1} The former consists of the very strong evidence, reviewed below, that hadrons are made of colored quarks which interact through the exchange of vector (spin one) gluons. Evidently the force must be color dependent, since we only see a single π meson rather than the nine different color combinations which can be made from a tricolored quark and antiquark. The only sensible (renormal-izable, unitary etc.) theory of vector gluons coupled to color is QCD [or a color gauge theory based on SO(3) but this turns out to fail the *a posteriori* tests and will not be discussed further].

## Keywords

Total Cross Section Chiral Symmetry Deep Inelastic Scattering Renormalization Group Equation Chiral Limit## Preview

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## References

- 1.Since these lectures are of an introductory nature many of the references are to reviews, where further references may be found, rather than to the original literature. For reviews of QCD see e.g. W. Marciano and H. Pagels, Phys. Rep. 36:137 (1978);ADSCrossRefGoogle Scholar
- 1a.G. Altarelli, Phys. Rep. 81:1 (1982);ADSCrossRefGoogle Scholar
- 1b.C.H. Llewellyn Smith, Phil. Trans. Roy. Soc. 304:5 (1982);CrossRefGoogle Scholar
- 1c.H. D. Politzer, to be published in Proc. XXI International Conference on High Energy Physics, Paris 1982.Google Scholar
- 2.R. Feist, in: “Proc. 1981 Symposium on Lepton and Photon Interactions at High Energy,” W. Pfeil, ed., University of Bonn, Bonn (1981).Google Scholar
- 3.S. L. Adler, in: “Lectures on Elementary Particles and Quantum Field Theory,” S. Deser, M. Grisaru and H. Pendelton, eds., MIT Press, Cambridge (1970);Google Scholar
- 3.R. Jackiw, in: “Lectures on Current Algebra and its Applications,” by S. Teiman, R. Jackiw and D. Gross, Princeton University Press, Princeton (1972).Google Scholar
- 4.V. De Alfaro et al., “Currents in Hadron Physics”, North-Holland, Amsterdam (1973);Google Scholar
- 4a.H. Pagels, Phys. Rep. 5:219 (1975).MathSciNetADSCrossRefGoogle Scholar
- 5.D. J. Gross and F. Wilczek, Phys. Rev. Lett. 30:1343 (1973);ADSCrossRefGoogle Scholar
- 5a.H. D. Politzer, Phys. Rev. Lett. 30:1346 (1973).ADSCrossRefGoogle Scholar
- 6.R. P. Feynman, in: “Weak and Electromagnetic Interactions at High Energy,” R. Balian and C. H. Llewellyn Smith, eds., North Holland, Amsterdam (1977).Google Scholar
- 7.A. De Rujula, H. Georgi and S. L. Glashow, Phys. Rev. D12:147(1975);ADSGoogle Scholar
- 7.N. Isgur, in: “Proc. Madison Conference on High Energy Physics,” L. Durand and L. G. Pondrom, eds., Madison (1980).Google Scholar
- 8.C. Rebbi, to be published in “Proc. XXI International Conference on High Energy Physics,” Paris 1982, and references therein.Google Scholar
- 9.The discussion in this section is simplified e.g. I have ignored external line corrections and subtleties such as gauge dependence. For a proper discussion see any modern book on quantum field theory, for example, C. Itzykson and J.-B. Zuber, “Quantum Field Theory,” McGraw Hill, New York (1980).Google Scholar
- 10.See Refs. 1 and A. H. Mueller, Phys. Rep. 73:237 (1981);ADSCrossRefGoogle Scholar
- 10.Yu. L. Dokshitser et al., Phys. Rep. 58:269 (1980)ADSCrossRefGoogle Scholar
- 10.E. Reya, Phys. Rep. 69:195 (1981).ADSCrossRefGoogle Scholar
- 10a.For a more detailed discussion from a similar point of view to that followed in these lectures see C. H. Llewellyn Smith, to be published in Proc. 1981 NATO Banff Summer Institute.Google Scholar
- 11.T. Kinoshita, J. Math. Phys. 3:650 (1962);ADSMATHCrossRefGoogle Scholar
- 11a.T. D. Lee and M. Nauenberg, Phys. Rev. 133:B1349 (1964).MathSciNetCrossRefGoogle Scholar
- 12.G. T. Bodwin, S. Brodsky and G. P. Lepage, Phys. Rev. Lett. 47:1799 (1981) and S. Brodsky, this volume, have discovered effects which may spoil the stronger assumption, which has often been made, that the function which absorbs the m dependence is “universal” i.e. totally process independent.ADSCrossRefGoogle Scholar
- 13.For a general review of jet production in e
^{+}e^{-}annihilation, both on and off resonances, see K. H. Mess and B. H. Wiik, DESY preprint 82–011 (1982).Google Scholar - 14.Ch. Berger et al., Phys. Lett. 78B:176 (1978) and 82B:449 (1979).ADSGoogle Scholar
- 15.J. Bienlein, in: “Proc. 1981 Symposium on Lepton and Photon Interactions at High Energy”, W. Pfeil, ed., University of Bonn, Bonn (1981);Google Scholar
- 15a.B. Niczyporuk et. al., Zeit. Phys. C9:1 (1981).ADSGoogle Scholar
- 16.R. P. Feynman, “Photon-Hadron Interactions”, Benjamin, Reading (1972);Google Scholar
- 16a.F. E. Close, “An Introduction to Quarks and Partons”, Academic Press, London (1978);Google Scholar
- 1b6.C. H. Llewellyn Smith, in: “Hadron Structure and Lepton-Hadron Interactions”, M. Levy et al., eds., Plenum, New York (1979).Google Scholar
- 17.J. Kogut and L. Suskind, Phys. Rev. D9:697 and 3391 (1974).ADSGoogle Scholar
- 18.P. Bosetti et al., Nucl. Phys. B140:1 (1980);Google Scholar
- 18a.H. Anderson et al., Phys. Rev. Lett. 40:1061 (1978);ADSCrossRefGoogle Scholar
- 18b.J. G. H. de Groot et al., Zeit. Phys. Cl:143 (1979).Google Scholar
- 19.H. Wahl,
*loc. cit.*Google Scholar - 20.F. Eisele, to be published in “Proc. XXI International Conference on High Energy Physics,” Paris 1982.Google Scholar