Limits on the diffractive mass in strong coherent $γ^*$-nucleus scattering

TL;DR

The paper analyzes coherent γ^*A diffraction in the high-energy, saturated regime and proves that the diffractive mass remains of order the photon virtuality $Q$, with larger masses exponentially suppressed by Levin-Tuchin dynamics deep in saturation. By formulating a fixed-gap evolution equation for the diffractive amplitude $N^D_t(x_{01},y,y_0)$ and exploring both weak and strong scattering limits, it shows how gap constraints control the growth of diffractive mass and the cross section. The analysis connects the Kovchegov-Levin framework to a Levin-Tuchin suppression mechanism, clarifying how unitarity is preserved and how triple-pomeron coupling effectively vanishes when the gap is above the saturation scale. The results provide a coherent, quantitative picture of when and how strong diffractive diffraction can occur in γ^*A collisions and why large-mass diffractive states are disfavored in the saturation regime.

Abstract

An evolution equation for diffractive production with a definite rapidity gap is given. Coherent $γ^*A$ collisions in the unitarity (saturation) region are studied with the conclusion that the diffractive mass is always on the order of the $γ^*$ virtuality, $Q$, when the scattering is strong. Deep in the saturation region diffractive masses significantly greater than $Q$ are strongly suppressed by a Levin-Tuchin mechanism.

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