Breaking of k(perpendicular to) factorization for single jet production off nuclei

The linear k(perpendicular to) factorization is part and parcel of the perturbative QCD description of high-energy hard processes off free nucleons. In the case of heavy nuclear targets the very concept of nuclear parton density becomes ill-defined as exemplified by the recent derivation [N. N. Nikolaev, W. Schafer, B. G. Zakharov, and V. R. Zoller, J. Exp. Theor. Phys. 97, 441 (2003).] of nonlinear nuclear k(perpendicular to) factorization for forward dijet production in deep inelastic scattering off nuclei. Here we report a derivation of the related breaking of k(perpendicular to) factorization for single-jet processes. We present a general formalism and apply it to several cases of practical interest: open-charm and quark and gluon-jet production in the central to beam fragmentation region of gamma(*)p, gamma(*)A, pp, and pA collisions. We show how the pattern of k(perpendicular to) factorization breaking and the nature and number of exchanged nuclear pomerons do change within the phase space of produced quark and gluon jets. As an application of the nonlinear k(perpendicular to) factorization we discuss the Cronin effect. Our results are also applicable to the p(perpendicular to) dependence of the Landau-Pomeranchuk-Migdal effect for, and nuclear quenching of, jets produced in the proton hemisphere of pA collisions.