Soft Component of Hard Reactions and Nuclear Shadowing (DIS, Drell-Yan reaction, heavy quark production)

TL;DR

The article reveals that a soft leading-twist component significantly contributes to hard reactions (DIS, DY, heavy-quark production) when viewed in the target rest frame, manifesting as nuclear shadowing. It develops a light-cone, color-dipole formalism to capture color coherence and frame-dependent interpretations, introducing a universal scaling variable $n(x,Q^2)$ that collapses shadowing data across processes. The approach successfully describes DIS and DY shadowing with a common mechanism and makes concrete predictions for heavy-quark production, predicting notable charm suppression in nuclei. This framework challenges naive factorization and has implications for interpreting nuclear parton distributions and shadowing phenomena in high-energy processes.

Abstract

We consider deep-inelastic lepton scattering, Drell-Yan lepton pair and heavy quark production in the reference frame of the target. These reactions traditionally treated as hard have, however, a substantial leading twist soft contribution. One of the manifestations of such a soft component, nuclear shadowing, is overviewed.

Figures (4)

• Figure 1: Normalized by $1/A$ nucleus-to-nucleon ratio of the structure functions plotted versus scaling variable $n(x,Q^2)$, defined in (\ref{['8']}). The data are from nmc1nmc2.
• Figure 2: Born diagrams for lepton pair production.
• Figure 3: Comparison of the parameter-free calculation of nuclear shadowing in DY reaction with the E772 data.
• Figure 4: The additional to Fig. 2 Born diagrams for heavy quark production.