We argue that the process gamma+A-->J/psi+"gap"+X at large momentum transfer q(2) provides a quick and effective way to test the onset of a novel perturbative QCD regime of strong absorption for the ...interaction of small dipoles at the collider energies. We find that already the first heavy-ion run at the LHC will allow one to study this reaction with sufficient statistics via ultraperipheral collisions, hence probing the interaction of qq dipoles of sizes approximately 0.2 fm with nuclear media down to x approximately 10(-5).
We present predictions for the J/ψ and ρ meson production in the heavy ion ultraperipheral collisions (UPC) for the current energy 2.76 TeV at the LHC. Both total cross sections and cross sections ...with the neutron emission from one or both nuclei are presented. We also perform analysis of the RHIC ρ meson photoproduction data and emphasize importance of these data for testing the current model for nucleus breakup in the UPC.
In the framework of the leading order of perturbative QCD, we study exclusive photoproduction of ψ(2
S
) mesons in ultraperipheral proton-proton and nucleus-nucleus collisions at the LHC. We ...calculate the charmonium rapidity distributions and show that the analysis of the LHC experimental data allows one to significantly reduce uncertainties in the behavior of the gluon densities of the proton and nuclei at small
x
.
We analyze the interplay of the hard and soft interaction dynamics in the onset of the black body limit in the high energy hadron–hadron and hadron–nucleus collisions. We demonstrate that hard ...interactions of large x partons with the strong small x gluon fields result in a faster increase of the range of the impact parameters where interaction reaches the unitarity limit. At superhigh energies, far above the Greizen–Zatsepin–Kuzmin limit, the radius of hadronic interactions, proportional to ln(s/s0), significantly exceeds static radii of the interacting hadrons (nuclei) and the dependence of the high energy elastic hadron–hadron scattering cross section on the impact parameter b becomes universal leading to the ratios of total cross sections of hadron–hadron, hadron–nucleus, nucleus–nucleus collisions becoming equal to one. The same universality is also expected for the ratio of structure functions: F2A(x,Q2)/F2N(x,Q2)→1 at very small x. We analyze how increase of the interaction radii with energy changes the energy dependence of total, absorption and inelastic cross sections, and the distribution over the number of wounded nucleons in proton–nucleus collisions.
We provide predictions for the
J/
ψ coherent production in the peripheral heavy ion collisions at LHC and RHIC using the leading twist model of nuclear shadowing based on the QCD factorization ...theorem for diffraction and the HERA hard diffraction data. We demonstrate that for LHC kinematics this model leads to a bump-shape distribution in rapidity which is suppressed overall as compared to the expectations of the color transparency regime by a factor ∼6. This is a significantly larger suppression than that expected within the impact parameter eikonal model. Thus we show that the interaction of spatially small wave package for which the total cross section of interaction with nucleons is small is still strongly shadowed by nuclear medium in high energy processes.
(ProQuest: ... denotes formulae and/or non-USASCII text omitted; see image).We consider ... photoproduction in ion-ion ultraperipheral collisions (UPCs) at the LHC and RHIC in the coherent and ...incoherent quasielastic channels with and without accompanying forward neutron emission and analyze the role of nuclear gluon shadowing at small ..., ..., in these processes. We find that despite the good agreement between large nuclear gluon shadowing and the ALICE data in the coherent channel, in the incoherent channel, the leading twist approximation predicts the amount of nuclear suppression which is by approximately a factor of ... exceeds that seen in the data. We hypothesize that part of the discrepancy can be accounted for by the incoherent inelastic process of ... photoproduction with nucleon dissociation. To separate the high-photon-energy and low-photon-energy contributions to the ... cross section, we consider ion-ion UPCs accompanied by neutron emission due to electromagnetic excitation of one or both colliding nuclei. We describe the corresponding PHENIX data and make predictions for the LHC kinematics. In addition, in the incoherent quasielastic case, we show that the separation between the low-photon-energy and high-photon-energy contributions can be efficiently performed by measuring the correlation between the directions of ... and the emitted neutrons.
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