New Scaling Phenomena in Nuclear Structure Functions

Abstract

We consider the nuclear mass-number (A) dependence of the nuclear structure functions. We restrict ourselves to a two-component model, in which we assume the existence of an exotic component other than the normal nucleon component in nuclei. We find that there exist scaling phenomena and that the structure function of the exotic component should be independent of A. We also show that the A dependence of the nuclear structure function can be attributed to that of the surface-to-volume ratio which is incorporated in the probability of finding the exotic component in the nucleus.PACS numbers: 25.30.Fj, 13.60.Hb, 21.65. + f Aubert et al. l and Bodek et al. 2 have revealed that there is a significant difference between the nuclear structure functions per nucleon Ff e (x,(? 2 ) and F? (x,Q 2 ) which are obtained from deepinelastic lepton-iron and lepton-deuterium scattering at large four-momentum transfer Q. This fact tells us that the quark structure of the nucleus cannot be deduced only from that of a free nucleon and attracts the attention of both nuclear and highenergy physicists. Recently, new experimental data on the ratio R A (x,Q 2 ) of cross sections per nucleon for deep-inelastic lepton scattering off various nuclei A to that off deuterium have been reported. 3 In this experiment, the ratios O-L /(T T of cross sections for absorption of longitudinal and transverse photons for various nuclei at Q 2 = 5 (GeV/c) 2 are also measured. Because <T L /O-T is small and has little A dependence, 3 we regard R A (x,Q 2 ) as the ratio of nuclear structure function per nucleon F A (x,Q 2 ) for nucleus A to F® (x,Q 2 ) for the deuteron. In recent experiments, 2,3 there is no significant Q 2 dependence in the region of 2.0 ^Q 2^ 15.0 (GeV/c) 2 and therefore we will use (? 2 -averaged ratio R A (x) and structure function F A (x).To explain "the EMC effect," many theoretical attempts have been proposed. 4 There is a class of models in which the existence of exotic components like extra pions or delta isobars, alpha clusters, or multiquark clusters in nuclei are assumed. The other class includes models in which nucleons in nuclei have lighter effective mass than the freenucleon mass 5 and the confinement size for quarks in a nucleus is larger than that in a usual nucleon. 6 .In this paper, we take the standpoint of the first class of the models and consider an exotic com-ponent other than the free-nucleon component in the nucleus. The new data provide us with information on the A dependence of the nuclear structure functions. In fact we found in these data new scaling phenomena which indicate that the exotic part of the nuclear structure function,

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“…Even if we use other models of the quark-to-hadron decay functions, the results will not differ much from that of (2,19). This form of the decay functions in (2·19) is consistent with the results 21 ) of the parton jet evolution in the leading log approximation of quantum chromo dynamics (QeD).…”

Effect of the Fermi motion on nuclear structure functions and the EMC effect

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Color Conductivity at High Resolution: A New Phenomenon of Nuclear Physics

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