696 research outputs found

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

The forward elastic scattering of light on light, {\em i.e.,} the reaction
$\gamma+\gamma \to \gamma+\gamma$ in the forward direction, is analyzed
utilizing real analytic amplitudes. We calculate $\rho_{\gamma \gamma}$, the
ratio of the real to the imaginary portion of the forward scattering amplitude,
by fitting the total $\gamma \gamma$ cross section data in the high energy
region $5 GeV \le \sqrt s \le 130$ GeV, assuming a cross section that rises
asymptotically as $\ln^2 s$. We then compare $\rho_{\gamma\gamma}$ to
$\rho_{nn}$, the ratio of the even portions of the $pp$ and \pbar p forward
scattering amplitudes, as well as to $\rho_{\gamma p}$, the $\rho$ value for
Compton scattering. Within errors, we find that the three $\rho$-values in the
c.m.s. energy region $5 GeV \le \sqrt s \le 130$ 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 $\gamma \gamma$ collisions

In this note we assess the validity and uncertainties in the predictions of
the eikonalised mini-jet model for $\sigma^{inel}_{\gamma \gamma}$. 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 $e^+e^-$
colliders, differ by about $\pm 25\%$. 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

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

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 $\gamma \gamma \to hadrons$ and compare it with OPAL and L3
data. We extrapolate this result to $\gamma p$ 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

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

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