187 research outputs found

    Charmonium suppression by gluon bremsstrahlung in p-A and A-B collisions

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    Prompt gluons are an additional source for charmonium suppression in nuclear collisions, in particular for nucleus-nucleus collisions. These gluons are radiated as bremsstrahlung in N-N collisions and interact inelastically with the charmonium states while the nuclei still overlap. The spectra and mean number of the prompt gluons are calculated perturbatively and the gluon-Psi inelastic cross section is estimated. The integrated cross sections for AB --> J/Psi (Psi')X for p-A and A-B collisions and the dependence on transverse energy for S-U and Pb-Pb can be described quantitatively with some adjustment of one parameter \sigma(gPsi).Comment: 17 pages of Latex including 10 figure

    Electroproduction of Charmonia off Protons and Nuclei

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    Elastic virtual photoproduction of charmonia on nucleons is calculated in a parameter free way with the light-cone dipole formalism and the same input: factorization in impact parameters, light-cone wave functions for the photons and the charmonia, and the universal phenomenological dipole cross section which is fitted to other data. The charmonium wave functions are calculated with four known realistic potentials, and two models for the dipole cross section are tested. Very good agreement with data for the cross section of charmonium electroproduction is found in a wide range of ss and Q2Q^2. Using the ingredients from those calculations we calculate also exclusive electroproduction of charmonia off nuclei. Here new effects become important, (i) color filtering of the ccˉc\bar c pair on its trajectory through nuclear matter, (ii) dependence on the finite lifetime of the ccˉc\bar c fluctuation (coherence length) and (iii) gluon shadowing in a nucleus compared to the one in a nucleon. Total coherent and incoherent cross sections for C, Cu and Pb as functions of ss are presented. The results can be tested with future electron-nucleus colliders or in the peripheral collisions of relativistic heavy ions.Comment: Talk at 2-nd International Workshop on Hadron Physics, 25-29 September 2002, Coimbra, Portugal. To appear in the Workshop Proceedings (will be published by the American Institute of Physics

    Imaging Localized States in Graphene Nanostructures

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    Probing techniques with spatial resolution have the potential to lead to a better understanding of the microscopic physical processes and to novel routes for manipulating nanostructures. We present scanning-gate images of a graphene quantum dot which is coupled to source and drain via two constrictions. We image and locate conductance resonances of the quantum dot in the Coulomb-blockade regime as well as resonances of localized states in the constrictions in real space.Comment: 18 pages, 7 figure

    For cost-reducing technologies, knowing markets is to change them

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    Journal ArticleSponsored research from a NSF Foundation/Whitaker Foundation initiative on cost-reducing technologies brought together faculty from engineering, medicine, and social sciences to link economic and policy assessments to engineering design. The technology under development is to be an inexpensive, easy-to-use monitor for self-management of metabolic diseases by patients, with specific application to phenylketonuria (PKU). While the technology remains in development, the experience, including discussions with others in the Whitaker and National Science foundations' program, raised interesting issues about economics, policy, and cost-reducing technologies

    J/ψJ/\psi suppression in Pb+Pb collisions and pTp_T broadening

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    We have analysed the NA50 data, on the centrality dependence of pTp_T broadening of J/ψJ/\psi's, in Pb+Pb collisions, at the CERN-SPS. The data were analysed in a QCD based model, where J/ψJ/\psi's are suppressed in 'nuclear' medium. Without any free parameter, the model could explain the NA50 pTp_T broadening data. The data were also analysed in a QGP based threshold model, where J/ψJ/\psi suppression is 100% above a critical density. The QGP based model could not explain the NA50 pTp_T broadening data. We have also predicted the centrality dependence of J/ψJ/\psi suppression and pTp_T broadening at RHIC energy. Both the models, the QGP based threshold model and the QCD based nuclear absorption model, predict pTp_T broadening very close to each other.Comment: The paper was completely revised. The conclusion is also changed. 5 pages, 4 figure