Hard Scattering in a Nuclear Environment: Farewell to Linear $k_{\perp }$-Factorization

Abstract

We discuss a dramatic change brought into the pQCD description of hard processes in a nuclear environment by a large thickness of heavy nuclei. It breaks the familiar linear $k_{\perp }$-factorization which must be replaced by a new concept of the nonlinear $k_{\perp }$-factorization introduced in \cite{Nonlinear}.We demonstrate the salient features of nonlinear $k_{\perp }$-factorization on several examples from hard dijet production in DIS off heavy nuclei to single-jet to dijet production in hadron-nucleus collisions >. We also comment briefly on the non-linear BFKL evolution for gluon density of nuclei.

Comments: 12 pages, 4 fgures, prepared for the Proceedings of the Workshop on Hadron Structure and QCD: from LOW to HIGH energies, St. Petersburg, Repino, Russia, 18-22 May 2004