Forward Physics in Proton-Nucleus and Nucleus-Nucleus Collisions

TL;DR

This paper presents a universal explanation for nuclear suppression in various high-energy nuclear reactions, attributing it to energy conservation rather than coherence effects, supported by model predictions and data agreement.

Contribution

It introduces a unified, energy conservation-based framework for nuclear suppression across multiple reactions, challenging the coherence or Color Glass Condensate interpretation.

Findings

Suppression occurs even at low energies where coherence is absent.

Model predictions align well with experimental data.

Suppression is primarily due to energy conservation, not coherence effects.

Abstract

We present an universal treatment for a substantial nuclear suppression representing a common feature of all known reactions on nuclear targets (forward production of high-pT hadrons, production of direct photons, the Drell-Yan process, heavy flavor production, etc.). Such a suppression at large Feynman xF, corresponding to region of minimal light-cone momentum fraction variable x2 in nuclei, is tempting to interpret as a manifestation of coherence or the Color Glass Condensate. We demonstrate, however, that it is actually a simple consequence of energy conservation and takes place even at low energies, where no effects of coherence are possible. We analyze this common suppression mechanism for several processes performing model predictions in the light-cone dipole approach. Our calculations agree with data.