Breaking of k⊥ factorization for single jet production off nuclei

The linear k_⊥ 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. NikolaevW. SchäferB. G. ZakharovV. R. Zoller, J. Exp. Theor. Phys.972003441] of nonlinear nuclear k_⊥ factorization for forward dijet production in deep inelastic scattering off nuclei. Here we report a derivation of the related breaking of k_⊥ 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 γ^*p, γ^*A, pp, and pA collisions. We show how the pattern of k_⊥ 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_⊥ factorization we discuss the Cronin effect. Our results are also applicable to the p_⊥ dependence of the Landau-Pomeranchuk-Migdal effect for, and nuclear quenching of, jets produced in the proton hemisphere of pA collisions.