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Particles and Fields

Eur. Phys. J. C 25, 287-289 (2002)
DOI: 10.1007/s10052-002-01019-6

Forward elastic scattering of light on light, $\gamma+\gamma\rightarrow\gamma+\gamma$

M.M. Block1 and G. Pancheri2

1  Department of Physics and Astronomy, Northwestern University, Evanston, IL 60208, USA
2  INFN-Laboratori Nazionali di Frascati, 00044 Frascati, Italy

(Received: 18 June 2002 / Published online: 9 August 2002 )

The forward elastic scattering of light on light, i.e., the reaction $\gamma+\gamma\rightarrow\gamma+\gamma$ 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\ {\rm 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 $\bar pp$ forward scattering amplitudes, as well as to $\rho_{\gamma p}$ [CITE], the $\rho$ value for Compton scattering. Within errors, we find that the three $\rho$-values in the c.m.s. energy region $5\ {\rm GeV}\le
\sqrt s\le 130 $ GeV are the same, as predicted by a factorization theorem of Block and Kaidalov [CITE].

© Società Italiana di Fisica, Springer-Verlag 2002