Gluon production in current-nucleus and nucleon-nucleus collisions in a quasi-classical approximation

TL;DR

The paper develops a quasi-classical, small-x framework for gluon production in current-nucleus and nucleon-nucleus collisions, contrasting covariant-gauge final-state interactions with gauge-dependent wavefunction effects in a large nucleus. It demonstrates that in the quasi-classical limit the nuclear gluon distribution is additive with $xG_A(x,Q^2) = A\,xG(x,Q^2)$ for regimes where coherence effects are limited, and shows how the produced gluon spectrum is described either by multiple scattering of a local production in covariant gauge or directly by the nucleus WW field in light-cone gauge. It provides explicit formulas for unintegrated and integrated gluon distributions, and for cross sections in nucleon-nucleus collisions, including soft and central-region production and a purely classical-field description without final-state interactions. The work clarifies gauge dependence in high-energy nuclear gluon production, connects WW field physics to observable spectra, and lays groundwork for understanding saturation effects and small-x dynamics in heavy nuclei.

Abstract

We calculate gluon production in deep inelastic scattering of the current j= - (1/4) F_{μν}^a F_{μν}^a off a large nucleus and in nucleon-nucleus collisions. In a covariant gauge calculation the transverse momentum spectrum of the gluon is determined by the final state interactions of the gluon with the nucleons in the nucleus. In a light-cone gauge calculation final state interactions are absent and these effects come from the light-cone wavefunction of the nucleus. We work in an approximation which neglects QCD evolution of gluons in the nucleon, that is in a quasi-classical approximation.

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