Coherent rho and J/psi photoproduction in ultraperipheral processes with electromagnetic dissociation of heavy ions at RHIC and LHC

We present predictions for the J/psi and rho 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 analyse the RHIC rho meson photoproduction data and emphasize importance of these data to test the current model for nucleus break up in UPC.Comment: 16 pages, 7 figure

Color Coherent Phenomena with Hadron Beams

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. A number of new experiments are suggested to probe color fluctuations in hadrons.Comment: 14 pages,6 figures,Dedicated to Koichi Yazaki on the occasion of his 60th birthday. Invited talk at KEK-Tanashi International Symposium on Physics of Hadrons and Nuclei, Tokyo, Japan, 14-17 Dec 199

Elastic and large t rapidity gap vector meson production in ultraperipheral proton-ion collisions

We evaluate the cross sections for the production of vector mesons in exclusive ultraperipheral proton-ion collisions at LHC. We find that the rates are high enough to study the energy and momentum transfer dependence of vector mesons - rho,phi, J/psi, Upsilon photoproduction in gamma p scattering in a wide energy range extending the measurements which were performed at HERA, providing new information about interplay of soft and hard physics in diffraction. Also, we calculate the contributions to the vector meson yield due to production of vector mesons off nuclear target by photons emitted by proton. We find, that least in the case of Upsilon production it is feasible to observe simultaneously both these processes. Such measurements would increase the precision with which the A-dependence of exclusive onium production can be determined. This would also enable one to estimate the amount of nuclear gluon shadowing of generalized gluon distributions at much smaller x than that is possible in AA collisions and to measure the cross sections for photoproduction processes in a significantly wider energy range than that achieved in experiments with fixed nuclear targets. We also present the cross section for vector meson production in pA collisions at RHIC. In addition, we consider production of vector mesons off protons with large rapidity gaps and large t. These processes probe small x dynamics of the elastic interaction of small dipoles at high energies and large but finite t, that is in the kinematics where DGLAP evolution is strongly suppressed. We estimate that this process could be studied at LHC up to W ~1 TeV with detectors which will be available at LHC.Comment: 21 pages, 9 figures, a reference to experimental data is adde

Leading twist coherent diffraction on nuclei in deep inelastic scattering at small x and nuclear shadowing

We extend the theory of leading twist nuclear shadowing to calculate leading twist nuclear diffractive parton distribution functions (nDPDFs). We observe that the quark and gluon nPDFs have different patterns of the $A$-dependence. It is found that the probability of diffraction in the quark channel increases with $A$, reaching about 30% at $x \sim 10^{-4}$ for $A \sim 200$, and weakly decreases with $Q^2$. In the gluon channel, the probability of diffraction is large for all nuclei ($\sim 40$% for heavy nuclei at $x \sim 10^{-4}$ and $Q_0^2 \sim 4$ GeV$^2$), it weakly depends on $A$ and it decreases rather fast with increasing $Q^2$ -- the probability decreases by approximately a factor of two as $Q^2$ changes from 4 GeV$^2$ to 100 GeV$^2$. We also find that nuclear shadowing breaks down Regge factorization of nDPDFs, which is satisfied experimentally in the nucleon case. All these novel effects in nDPDFs are large enough to be straightforwardly measured in ultraperipheral collisions at the LHC.Comment: 14 pages, 7 figures. Extended discussion. Final version published in PL

Diffraction at HERA, Color Opacity and Nuclear Shadowing

The QCD factorization theorem for diffractive processes in DIS is used to derive formulae for the leading twist contribution to the nuclear shadowing of parton distributions in the low thickness limit. Based on the current analyzes of diffraction at HERA we find that the average strength of the interactions which govern diffraction in the gluon sector at $x \le 10^{-3}, Q_0=2 GeV$ is ~50 mb. This is 3 times larger than in the quark sector and suggests that applicability of DGLAP approximation requires significantly larger $Q_0$ in the gluon sector. We use this information to estimate quark and gluon shadowing for heavy nuclei and to calculate its$Q^2$ depen- dence. For A~200 the amount of the gluon shadowing: $G_A/AG_N\sim 0.25-0.4$ at $x<10^{-3},Q=2GeV$ is sensitive to the probability of the small size configurations within wave function of the gluon "partonometer" at the $Q_0$ scale. At this scale for $A\sim 200$ the nonperturbative contribution to the gluon density is reduced by a factor of 4-5 at $x \le 10^{-3}$ unmasking PQCD physics in the gluon distribution of heavy nuclei. Such shadowing would strongly modify the first stage of the heavy ion collisions at LHC, and would lead to large color opacity effects in $eA$ collisions at x<0.001. The leading twist contribution to the cross section of the coherent $J/\psi$ production off $A\ge 12$ nuclei at $\sqrt s \ge 70$ GeV is strongly reduced as compared to the naive color transparency expectations. The Gribov black body limit for $F_{2A}(x,Q^2)$ is extended to the case of the gluon distributions in nuclei and shown to be relevant for the HERA kinematics of $eA$ collisions. Properties of the final states are also briefly discussed.Comment: 42 pages, 10 figures, final version to appear in Europ. Jour.of Phys., discussion of a number of issues is substantially extended, two figures and several references are adde

Single particle strength restoration and nuclear transparency in high Q^2 exclusive (e,e'p) reactions

Quenching of the single particle strength which previously precluded unambiguous measurement of nuclear transparency in quasifree (e,e'p) reactions at high momentum transfer is evaluated from the cross sections of measured processes. We have demonstrated evidence of the single particle strength restoration with increase of the momentum transfer in exclusive (e,e'p) reactions and argue that in practically interesting cases of study the nuclear transparency in these processes quenching is weakly depends on the probability of short range nucleon correlations. It is shown that use of Glauber approximation well describes NE18 and E94-139 (e,e'p) data at the momentum transfers 1 GeV^2 < Q^2 < 3 GeV^2. This gives a further support to our observation that the quenching of nuclear levels strongly depends on the resolution (Q^2)and practically disappears at Q^2>1GeV^2.Comment: 15 pages, 5 figures; references added, discussion extende

A fresh look at diffractive J/ψJ/\psi photoproduction at HERA, with predictions for THERA

We quantify perturbative and non-perturbative QCD effects in the exclusive $J/\psi$-photoproduction cross section, and in the shrinkage of the differential cross section with respect to momentum transfer, $t$. We predict that in the high energy THERA region there will always be a significant contribution to this process that rises quickly with energy. This implies that the taming of the rise of the cross section with energy, due to both the expansion of spatially-small fluctuations in the photon and to higher twist effects, is rather gradual.Comment: Published version, 29 pages, 16 figures, uses JHEP.cls. Substantially rewritten to better emphasize the generality of the results in response to the referee's comments. Predictions for MRST LO partons added, calculations and discussion of the real part of the amplitude and of alpha prime improved. Five of the original figures modified. Two new plots, of the dipole cross section for two different values of parameter lambda, and of energy dependence of alpha prime, added. Three additional references include