697 research outputs found

    Forward Elastic Scattering of Light on Light, \gamma+\gamma\to\gamma+\gamma

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    The forward elastic scattering of light on light, {\em i.e.,} the reaction γ+γγ+γ\gamma+\gamma \to \gamma+\gamma in the forward direction, is analyzed utilizing real analytic amplitudes. We calculate ργγ\rho_{\gamma \gamma}, the ratio of the real to the imaginary portion of the forward scattering amplitude, by fitting the total γγ\gamma \gamma cross section data in the high energy region 5GeVs1305 GeV \le \sqrt s \le 130 GeV, assuming a cross section that rises asymptotically as ln2s\ln^2 s. We then compare ργγ\rho_{\gamma\gamma} to ρnn\rho_{nn}, the ratio of the even portions of the pppp and \pbar p forward scattering amplitudes, as well as to ργp\rho_{\gamma p}, the ρ\rho value for Compton scattering. Within errors, we find that the three ρ\rho-values in the c.m.s. energy region 5GeVs1305 GeV \le \sqrt s \le 130 GeV are the same, as predicted by a factorization theorem of Block and Kadailov.Comment: 5 pages, Latex2e, 2 postscript figures, uses epsfig.st

    Eikonalized mini-jet cross-sections in γγ\gamma \gamma collisions

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    In this note we assess the validity and uncertainties in the predictions of the eikonalised mini-jet model for σγγinel\sigma^{inel}_{\gamma \gamma}. We are able to find a choice of parameters where the predictions are compatible with the current data. Even for this restricted range of parameters the predictions at the high c.m. energies, which can be reached at the TeV energy e+ee^+e^- colliders, differ by about ±25%\pm 25\%. LEP 2 data can help pinpoint these parameters and hence reduce the uncertainties in the predictions.Comment: 5 pages, latex, requires epsfig.sty, a4wide.sty, full ps file available at http://hpteor.lnf.infn.it/pancheri/lc2000.p

    Total Cross-sections

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    We examine the energy dependence of total cross-sections for photon processes and discuss the QCD contribution to the rising behaviourComment: 5 pages, LaTeX, 2 figures, talk presented by G. Pancheri at Photon - 2001, The International Conference on Structure and Interactions of Photons, Ascona, Sept. 2-7,2001. To appear in the proceeding

    Total Photonic and Hadronic Cross-sections

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    We discuss total cross-sections within the context of the QCD calculable mini-jet model, highlighting its successes and failures. In particular we show its description of γγhadrons\gamma \gamma \to hadrons and compare it with OPAL and L3 data. We extrapolate this result to γp\gamma p total cross-sections and propose a phenomenological ans\"atz for virtual photon cross-sections. We point out that the good agreement with data obtained with the Eikonal Minijet Model should not hide the many uncertainties buried in the impact parameter distribution. A model obtained from Soft Gluon Summation is briefly discussed and its application to hadronic cross-sections is shown.Comment: 10 pages, 5 figures, LaTeX, uses aipproc.sty. To appear in the proceedings of Photon 2000, Ambelside, U.K., Aug 2000. The title, the number of pages and the number of figures in the announcement were corrected to correspond to the submitted pape

    Photon-Photon total inelastic cross-section

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    We discuss predictions for the total inelastic gamma-gamma cross-section and their model dependence on the input parameters. We compare results from a simple extension of the Regge Pomeron exchange model as well as predictions from the eikonalized mini-jet model with recent LEP data.Comment: 7 pages, LateX, 2 eps figures. Talk presented at Photon'97, Egmond aan Zee, May 199