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Register a new userGluon Shadowing in DIS off Nuclei
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B.Z. Kopeliovich
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Within a light-cone quantum-chromodynamics dipole formalism based on the Green function technique, we study nuclear shadowing in deep-inelastic scattering at small Bjorken xB < 0.01. Such a formalism incorporates naturally color transparency and coherence length effects. Calculations of the nuclear shadowing for the bar{q}q Fock component of the photon are based on an exact numerical solution of the evolution equation for the Green function, using a realistic form of the dipole cross section and nuclear density function. Such an exact numerical solution is unavoidable for xB > 0.0001, when a variation of the transverse size of the bar{q}q Fock component must be taken into account. The eikonal approximation, used so far in most other models, can be applied only at high energies, when xB < 0.0001 and the transverse size of the bar{q}q Fock component is frozen during propagation through the nuclear matter. At xB < 0.01 we find quite a large contribution of gluon suppression to nuclear shadowing, as a shadowing correction for the higher Fock states containing gluons. Numerical results for nuclear shadowing are compared with the available data from the E665 and NMC collaborations. Nuclear shadowing is also predicted at very small xB corresponding to LHC kinematical range. Finally the model predictions are compared and discussed with the results obtained from other models.
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We present a revision of predictions for nuclear shadowing in deep-inelastic scattering at small Bjorken $x_{Bj}$ corresponding to kinematic regions accessible by the future experiments at electron-ion colliders. The nuclear shadowing is treated within the color dipole formalism based on the rigorous Green function technique. This allows incorporating naturally color transparency and coherence length effects, which are not consistently and properly included in present calculations. For the lowest $|qbar qrangle$ Fock component of the photon, our calculations are based on an exact numerical solution of the evolution equation for the Green function. Here the magnitude of shadowing is tested using a realistic form for the nuclear density function, as well as various phenomenological models for the dipole cross section. The corresponding variation of the transverse size of the $qbar q$ photon fluctuations is important for $x_{Bj}gtrsim 10^{-4}$, on the contrary with the most of other models, which use frequently only the eikonal approximation with the frozen transverse size. At $x_{Bj}lesssim 0.01$ we calculate within the same formalism also a shadowing correction for the higher Fock component of the photon containing gluons. The corresponding magnitudes of gluon shadowing correction are compared adopting different phenomenological dipole models. Our results are tested by available data from the E665 and NMC collaborations. Finally, the magnitude of nuclear shadowing is predicted for various kinematic regions that should be scanned by the future experiments at electron-ion colliders.
In this work we analyse the entanglement entropy in deep inelastic scattering off protons and nuclei. It is computed based on the formalism where the partonic state at small-x is maximally entangled with proton being constituted by large number of microstates occuring with equal probabilities. We consider analytical expressions for the number of gluons, N_{gluon}, obtained from gluon saturation models for the dipole-target amplitudes within the QCD color dipole picture. In particular, the nuclear entanglement entropy per nucleon is studied. We also study the underlying uncertainties on these calculations and compare the results to similar investigations in literature.
We calculate shadowing using new data on the gluon density of the Pomeron recently measured with high precision at HERA. The calculations are made in a Glauber-Gribov framework and Pomeron tree-diagrams are summed up within a unitarity-conserving procedure. The total cross section of $vphot A$ interaction is then found in a parameter-free description, employing gluon diffractive and inclusive distribution functions as input. A strong shadowing effect is obtained, in good agreement with several other models. Impact parameter dependence of gluon shadowing is also presented.
We study the relevance of experimental data on heavy-flavor [$D^0$, $J/psi$, $Brightarrow J/psi$ and $Upsilon(1S)$ mesons] production in proton-lead collisions at the LHC to improve our knowledge of the gluon-momentum distribution inside heavy nuclei. We observe that the nuclear effects encoded in both most recent global fits of nuclear parton densities at next-to-leading order (nCTEQ15 and EPPS16) provide a good overall description of the LHC data. We interpret this as a hint that these are the dominant ones. In turn, we perform a Bayesian-reweighting analysis for each particle data sample which shows that each of the existing heavy-quark(onium) data set clearly points --with a minimal statistical significance of 7 $sigma$-- to a shadowed gluon distribution at small $x$ in the lead. Moreover, our analysis corroborates the existence of gluon antishadowing. Overall, the inclusion of such heavy-flavor data in a global fit would significantly reduce the uncertainty on the gluon density down to $xsimeq 7times 10^{-6}$ --where no other data exist-- while keeping an agreement with the other data of the global fits. Our study accounts for the factorization-scale uncertainties which dominate for the charm(onium) sector.
We present and discuss the theory and phenomenology of the leading twist theory of nuclear shadowing which is based on the combination of the generalization of the Gribov-Glauber theory, QCD factorization theorems, and the HERA QCD analysis of diffraction in lepton-proton deep inelastic scattering (DIS). We apply this technique for the analysis of a wide range of hard processes with nuclei---inclusive DIS on deuterons, medium-range and heavy nuclei, coherent and incoherent diffractive DIS with nuclei, and hard diffraction in proton-nucleus scattering---and make predictions for the effect of nuclear shadowing in the corresponding sea quark and gluon parton distributions. We also analyze the role of the leading twist nuclear shadowing in generalized parton distributions in nuclei and in certain characteristics of final states in nuclear DIS. We discuss the limits of applicability of the leading twist approximation for small x scattering off nuclei and the onset of the black disk regime and methods of detecting it. It will be possible to check many of our predictions in the near future in the studies of the ultraperipheral collisions at the Large Hadron Collider (LHC). Further checks will be possible in pA collisions at the LHC and forward hadron production at the Relativistic Heavy Ion Collider (RHIC). Detailed tests will be possible at an Electron-Ion Collider (EIC) in the USA and at the Large Hadron-Electron Collider (LHeC) at CERN.
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