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Article
Title	Two-photon collisions at LEP
Author(s)	Hsiang Nan Li
Affiliation	(Inst of Phys, Acad Sinica, Taipei, Taiwan)
Publication	2003
In:	Int. J. Mod. Phys. A 18, 8 (2003) pp.1421-4
In:	3rd Circum-Pan-Pacific Symposium on High Energy Spin Physics, Beijing, China, 8 - 13 Oct 2001, pp.1421-4
Subject category	Particle Physics - Phenomenology
Abstract	We study the effect of initial-state radiation in the double-tagged process ee to ee + hadrons by introducing the parton distribution functions associated with an electron, a positron, and a photon, which satisfy a set of Dokshitzer-Gribov-Lipatov-Altarelli-Parisi (DGLAP) equations. It is observed that the radiation effect is not essential in most of the kinematic range. This observation applies to the subprocess of two-photon collision via quark exchange and via onium scattering. The deviation of the LEP data from the prediction for quark exchange at large rapidity may be regarded as a sign of new mechanism, such as the Balitskii-Fadin-Kuraev-Lipatov mechanism. (15 refs).