Application of the constituent quark exchange model to the parton distributions and the EMC ratios of 12C and 14N nuclei

Abstract

The quark exchange model (QEM) is reformulated for the A=12 and 14 systems to obtain the constituent quark distributions of C12 and N14 nuclei, respectively. Afterwards, the different types of the point-like parton distribution functions (PDFs), i.e., the valence quarks, the sea quarks and the gluons, are extracted from the constituent quark model (CQM), at the hadronic scale Q02=0.34 GeV2 to generate the constituent quark exchange model (CQEM = QEM ⊕ CQM) PDFs. From the resulted PDFs, the structure functions and the European Muon Collaboration (EMC) ratios of the above-mentioned nuclei at the appropriate hadronic scale are calculated. To make our results more comparable with the available experimental data, we evolve the PDFs, by using the standard Dokshitzer–Gribov–Lipatov–Altarelli–Parisi (DGALP) evolution equations, to the higher hard scales. Subsequently, the EMC ratios of C12 and N14 nuclei at some higher energy scales, corresponding to the scales of available data, are calculated, at the leading (LO) and the next-to-leading (NLO) orders of pQCD. By doing so, it is observed that the EMC ratios do not significantly depend on the hard scale Q2, and the outcomes are consistent with the various experimental data such as HERMES, BCDMS, JLab, SLAC, NMC, and EMC. Especially, in the mid-range of Bjorken x values, the results are so desirable. Like our previous works for the H4e and L6i nuclei, we again observe that at a fixed scale Q2, the LO and the NLO EMC ratios with high precision are approximately the same. Therefore, one can conclude that at a given hard scale, the LO approximation is good enough for calculating the EMC ratios of light nuclei.