The First EMC effect

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The first EMC effect [1] shows that if the quark deep inelastic data of heavier nuclei are compared to those of the deuteron, then one finds that data of the heavier nucleus are located in a smaller x region. This property means that the Fermi motion of quarks of a heavy nucleus is smaller than that of the deuteron's quarks. Hence, one conclusion inferred from the first EMC effect is the increase of the self volume occupied by quarks in nuclei together with the increase in number of nucleons A. (Note that, excluding a very small number of light nuclei, nucleon density of nuclei practically takes the same value.)

The nucleus - liquid drop similarity of the regular monopole theory easily explains this effect. Thus, in liquids (and in solids) electrons of a neighboring atom (denoted by B) penetrate the volume of the atom examined here (denoted by A). Thus, the attractive field of the nucleus of A is partially screened by electrons of B. Hence, electrons of A "see" a smaller attractive force and settle in a larger volume. In nuclei, the first EMC effect is the magnetic monopole analog of this effect: just replace the nucleus by the baryonic core and the electrons by quarks.

The first EMC effect was discovered about a decade after the formulation of QCD. In spite of this fact, proponents of QCD did not predict this effect. Thus the first EMC effect is described in its first report by the following words [1]: "The observed x-dependence of this ratio is in disagreement with existing theoretical predictions." Moreover, an acceptable explanation of the first EMC effect cannot be found in standard QCD textbooks. The lack of an adequate QCD explanation for this effect is stated in the literature [2]. Furthermore, a recent CERN publication declares: the EMC data still puzzle QCD supporters. For details, click here.


[1] J. J. Aubert et al., Phys. Lett. B123, 275 (1983).

[2] J. Arrington et al., J. Phys. Conference Series, 69, 012024 (2007).