11,749 research outputs found

    Diffractive photoproduction of Upsilon states at HERA

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    Cross sections for the diffractive photoproduction of the Upsilon-family at HERA energies, within the framework of the analysis by Frankfurt, Koepf and Strikman, are presented. They compare well with the recent preliminary data from ZEUS and H1. Two novel effects lead to a significant enhancement of the original calculation: the non-diagonal (or skewed) kinematics, calculated to leading-log(Q^2) accuracy, and the large magnitude of the real part of the amplitude. A considerably stronger rise in energy is predicted than that found in J/Psi-production.Comment: Talk at DIS99, April 1999, Zeuthen, Berlin. Latex, 3 pages, 2 figure

    Color Coherent Phenomena with Hadron Beams

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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. 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

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    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

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    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 AA-dependence. It is found that the probability of diffraction in the quark channel increases with AA, reaching about 30% at x∼10−4x \sim 10^{-4} for A∼200A \sim 200, and weakly decreases with Q2Q^2. In the gluon channel, the probability of diffraction is large for all nuclei (∼40\sim 40% for heavy nuclei at x∼10−4x \sim 10^{-4} and Q02∼4Q_0^2 \sim 4 GeV2^2), it weakly depends on AA and it decreases rather fast with increasing Q2Q^2 -- the probability decreases by approximately a factor of two as Q2Q^2 changes from 4 GeV2^2 to 100 GeV2^2. 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

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

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    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

    Searching for Color Coherent Effects at Intermediate Q2Q^2 via Double Scattering Processes

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    We propose that measuring the Q2Q^2 dependence of the number of final-state interactions of the recoil protons in quasi-elastic electron scattering from light nuclei is a new method to investigate Color Coherent effects at {\bf intermediate} values of Q2Q^2 ({∼\sim few (GeV/c)2(GeV/c)^2}). This is instead of measuring events without final-state interactions. Our calculations indicate that such measurements could reveal significant color transparency effects for the highest of the energies initially available at CEBAF. Measurements that detect more than one hadron in the final state, which require the use of large acceptance (4Ï€4\pi) detectors, are required.Comment: 19 pages in RevTex, 5 postscript figures available from [email protected]

    High-energy hadron physics at future facilities

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    We outline several directions for future investigations of the three-dimensional structure of nucleon, including multiparton correlations, color transparency, and branching processes at hadron colliders and at hadron factories. We also find evidence that pQCD regime for non-vacuum Regge trajectories sets in for −t≥1GeV2-t\ge 1 {GeV}^2 leading to nearly t-independent trajectories.Comment: 8 pages, 1 figure, Invited talk at INPC07, Tokyo, June 3-8, 200

    Fading out of J/psi color transparency in high energy heavy ion peripheral collisions

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    We provide predictions for the J/psi coherent production in the peripheral heavy ion collisions at LHC and at 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 the 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 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.Comment: 13 pages, 7 figure

    Future Small x Physics with ep and eA Colliders

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    The interaction of spatially small dipoles with nucleons, nuclei is calculated in the DGLAP approximation at the top of HERA energies and found to be close to the SS-channel unitarity limit in the case of the color octet dipoles. The DGLAP analyses of the current diffractive data appear to support this conclusion as they indicate a ∼30−40\sim 30-40% probability of the gluon induced diffraction for Q2∼4Q^2\sim 4 GeV2^2. The need for the high-precision measurements of the tt-dependence of inclusive and exclusive diffraction for pinpointing higher twist effects in the gluon sector is emphasized.The eAeA collisions at HERA would provide a strong amplification of the gluon densities allowing to reach deep into the regime of nonlinear QCD evolution. Connection between the leading twist nuclear shadowing and leading twist diffraction in epep scattering is explained. The presented model independent results for the nuclear shadowing for light nuclei indicate much larger shadowing for the gluon sector than for the sea quark sector.It is argued that HERA in eAeA mode would be able to discover a number of new phenomena including large gluon shadowing, large nonlinearities in parton evolution, small xx color transparency in the vector meson production followed by color opacity at x≤.005x\le .005, large probability of inclusive diffraction. Implications for the nucleus-nucleus collisions at LHC are discussed as well.Comment: 17 pp, 12 fig. Plenary talk to be published in the proceedings of 7th International Workshop on Deep Inelastic Scattering and QCD (DIS 99), Zeuthen, Germany, 19-23 Apr 1999. Submitted to Nucl.Phys.Proc.Supp

    Energy losses in the black disc regime and correlation effects in the STAR forward pion production in dAu collisions

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    We argue that in the small x processes, in the black disc QCD regime (BDR) a very forward parton propagating through the nuclear matter should loose a significant and increasing with energy and atomic number fraction of its initial energy as a result of dominance of inelastic interactions, causality and energy-momentum conservation. We evaluate these energy losses and find them to lead to the significant suppression of the forward jet production in the central NA collisions at collider energies with a moderate suppression of recoiling jet at central rapidities. We confront our expectations with the recent RHIC data of the STAR collaboration on the probability, PP, for emission of at least one fast hadron at a central rapidity in association with production of a very forward high ptp_t neutral pion in pppp and dAudAu collisions. We calculate the A-dependence of PP, and find that the data imply a strong suppression of leading pion production at central impact parameters. We also conclude that production of recoil jets in the hard subprocess is not suppressed providing further evidence for the dominance of peripheral collisions. Both features of the data are consistent with the onset of BDR. We suggest new phenomena and new observables to investigate BDR at RHIC and LHC.Comment: 18 pages,final text to be published in Phys.Lett.B, evaluation of the fractional energy energy losses in the black disk regime is ellaborate
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