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Article
Report number	hep-ph/0304218
Title	Onset of Perturbative Color Opacity at Small x and Upsilon Coherent Photoproduction off heavy nuclei at LHC
Author(s)	Frankfurt, L L ; Guzey, V ; Strikman, M I ; Zhalov, M B
Affiliation	(Penn State U.) ; (Petersburg Nucl. Phys. Inst.) ; (Ruhr U., Bochum) ; (Tel Aviv U.)
Publication	2003
Imprint	23 Apr 2003
Number of pages	14
Note	Comments: 14 pages, 4 figures
In:	JHEP 08 (2003) 043
DOI	10.1088/1126-6708/2003/08/043
Subject category	Particle Physics - Phenomenology
Abstract	We study photon-induced coherent production of Upsilon in ultraperipheral heavy ion collisions at LHC and demonstrate that the counting rates will be sufficient to measure nuclear shadowing of generalized gluon distributions. This will establish the transition from the regime of color transparency to the regime of perturbative color opacity in an unambiguous way. We argue that such measurements will provide the possibility to investigate the interaction of ultra-small color dipoles with nuclei in QCD at large energies, which are beyond the reach of the electron-nucleon (nucleus) colliders, and will unambiguously discriminate between the leading twist and higher twist scenarios of gluon nuclear shadowing.

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