Leading twist nuclear shadowing: Uncertainties, comparison to experiments, and higher twist effects

Using the leading twist approach to nuclear shadowing, which is based on the relationship between nuclear shadowing and diffraction on a nucleon, we calculate next-to-leading order nuclear parton distribution functions (nPDFs) and structure functions in the region $0.2>x>{10}^{\ensuremath{-}5}$ and ${Q}^{2}\ensuremath{\ge}4\text{ }\text{ }{\mathrm{G}\mathrm{e}\mathrm{V}}^{2}$. The uncertainties of our predictions due to the uncertainties of the experimental input and the theory are quantified. We determine the relative role of the small ($\ensuremath{\sim}{Q}^{2}$) and large ($\ensuremath{\gg}{Q}^{2}$) diffractive masses in nuclear shadowing as a function of $x$ and find that the large mass contribution, which is an analog of the triple Pomeron exchange, becomes significant only for $x\ensuremath{\le}{10}^{\ensuremath{-}4}$. Comparing our predictions to the available fixed-target nuclear deep inelastic scattering data, we argue, based on the current experimental studies of the leading twist diffraction, that the data at moderately small $x\ensuremath{\sim}0.01$ and ${Q}^{2}\ensuremath{\sim}2\text{ }\text{ }{\mathrm{G}\mathrm{e}\mathrm{V}}^{2}$ could contain significant higher twist effects hindering the extraction of nPDFs from that data. Also, we find that the next-to-leading order effects in nuclear shadowing in the ratio of the nucleus to nucleon structure functions ${F}_{2}$ are quite sizable. Within the same formalism, we also present results for the impact parameter dependence of nPDFs. We also address the problem of extracting the neutron ${F}_{2n}(x,{Q}^{2})$ from the deuteron and proton data. We suggest a simple and nearly model-independent procedure of correcting for nuclear shadowing effects using ${F}_{2}^{A}/{F}_{2}^{D}$ ratios.

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