Cross sections of coherent light vector meson photoproduction in ultraperipheral proton-proton and proton-nucleus interactions on the Large Hadron Collider are calculated using the ...Donnachie-Landshoff model and the Weizsacker-Williams (equivalent photons) approach.
We evaluate the large momentum transfer J/ψ photoproduction with rapidity gaps in ultraperipheral proton–ion collisions at the LHC which provides an effective method of probing dynamics of large t ...elastic hard QCD Pomeron interactions. It is shown that the experimental studies of this process would allow to investigate the energy dependence of cross section of elastic scattering of a small cc¯ dipole off the gluon over a wide range of invariant energies 103<scc¯-gluon<106 GeV2. The accessible energy range exceeds the one reached in γp at HERA by a factor of 10 and allows the kinematic cuts which improve greatly sensitivity to the Pomeron dynamics as compared to the HERA measurements. The cross section is expected to change by a factor ⩾20 throughout this interval and our estimates predict quite reasonable counting rates for this process with the several of the LHC detectors.
We suggest the ratio of the ψ″(3770)/ψ′(3686) production cross sections as an unambiguous probe of the dominance of hard, point-like physics in charmonium production. If hard physics dominates the ...charmonium production the ratio: σ(ψ″)σ(ψ′)≈Γ(ψ″→l+l−)Γ(ψ′→l+l−)≈0.1 is independent of the process. We argue that since the dominant DD decay mode of the ψ″-meson can be detected with a high efficiency at the current facilities the effective counting rate for the ψ″ production should be comparable to that of the ψ′ and hence it could be observed at the B-factories. Even in hadron induced processes the ratio will not be changed significantly by final state interactions due to the similar mass and size of these two charmonium states. A possible exception are the charmonium state interactions with low energy particles—comovers—which are especially relevant for heavy ion collisions.
We show that the recent ALICE measurements of exclusive J/IJ/I production in ultraperipheral PbPb collisions at 2.76 TeV provide the first direct experimental evidence for the strong nuclear gluon ...shadowing in lead at xa1410a3xa1410a3. The evidence is based on the comparison of the nuclear suppression factor S(xa0.001)=0.61a0.04+0.05 found in the analysis of the coherent J/IJ/I photoproduction cross sections measured by ALICE with the nuclear gluon shadowing predicted by the global fits of nuclear parton distributions and by the leading twist theory of nuclear shadowing.
Based on accurate calculations of the flux of equivalent photons of the proton and heavy nuclei and the pQCD framework for the gluon distribution in the proton and nuclei, we analyze the rapidity and ...momentum transfer distributions of coherent J/psi photoproduction in ultraperipheral proton-Pb collisions at the LHC. We demonstrate that unlike the case of proton-proton UPCs marred by certain theoretical uncertainties and experimental limitations, after a cut excluding the region of small momentum transfers, ultraperipheral proton-Pb collisions offer a clean way to study the gluon distribution in the proton down to xasymptotically =10^sup -5^. Our analysis of the momentum transfer distributions shows that an interplay of J/psi production by low-energy photons on the nucleus and by high-energy photons on the proton in proton-Pb UPCs can result in some excess of events at small p ^sub t^ in a definite region of the rapidity y.
Using the framework of collinear factorization in perturbative QCD (pQCD), we analyze the recent data of the LHCb and ALICE collaborations on exclusive photoproduction of J/psi in ultraperipheral pp ...and AA collisions, respectively. We demonstrate that the simultaneous analysis of the proton and Pb data allows us to reduce the ambiguity of the pQCD description of the γp arrow right J/psip and γA arrow right J/psiA cross sections and, hence, to place additional constraints on the gluon distributions in the nucleon and nuclei at small x. We also make predictions for the cross section of coherent exclusive photoproduction of J/psi in nucleus-nucleus ultraperipheral collisions accompanied by the electromagnetic excitation of nuclei and the subsequent neutron emission.
The processes of coherent and incoherent charmonium photoproduction in ion–ion and proton–ion ultraperipheral collisions at the LHC are discussed. A description of these processes in the context of ...the QCD perturbative theory is examined to determine the effects of nuclear shadowing in the nuclear gluon density at small
x
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We outline major ideas involved in discussion of color coherence phenomena (CCP) at intermediate energies. We point out that the recent advances in calculating cross sections of hard exclusive ...processes off light nuclei allow to use the lightest nuclei for sensitive tests of CCP. Consistency of the results of the measurements of color transparency in quasielastic A(p,2p) and A(e,e′p) processes is emphasized. Evidence for presence of significant color fluctuations in nucleons and pions emerging from the study of diffractive processes is summarized. A new class of hard processes leading to three particle final state is suggested for electron and hadron projectiles.
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