Nuclear enhancement of universal dynamics of high parton densities

TL;DR

It is shown that the enhancement of the saturation scale in large nuclei relative to the proton is significantly influenced by the effects of quantum evolution and the impact parameter dependence of dipole cross sections in high energy QCD.

Abstract

We show that the enhancement of the saturation scale in large nuclei relative to the proton is significantly influenced by the effects of quantum evolution and the impact parameter dependence of dipole cross sections in high energy QCD. We demonstrate that there is a strong A dependence in diffractive deeply inelastic scattering and discuss its sensitivity to the measurement of the recoil nucleus.

Figures (5)

• Figure 1: Left: Predictions for shadowing compared to NMC data. Center: predictions for $12F_2^\textrm{Sn}/118F_2^\textrm{C}$ compared to NMC data at ${x} = 0.0125$. Right: Likewise for $Q^2 = 5 \textrm{ GeV}^2$ as a function of ${x}$.
• Figure 2: Impact parameter dependence of the saturation scale for p, Ca and Au at ${x} = 0.001$ and $Q^2 = 1 \textrm{ GeV}^2$. Details in text.
• Figure 3: Saturation scale at $b = 0$ (open symbols) and $b=b_\textrm{med.}$ (filled symbols) as a function of $A$ for different ${x}$. The saturation scale for the proton is shown at $A=1$ and by the arrows on the right. Left: IPsat model. Right: bCGC model.
• Figure 4: The $t$-dependence of the calcium and the proton dipole cross sections. The "breakup" curve for calcium is computed using $\frac{1}{16 \pi} \left\langle |{ \sigma_\textrm{dip} }({x},r,{\boldsymbol{\Delta}_\perp})|^2 \right\rangle_\textrm{N}$ for $r = 0.2\textrm{ fm}$ and ${x} = 0.001$ and "no breakup" curve using $\frac{1}{16 \pi} \left\langle { \sigma_\textrm{dip} }({x},r,{\boldsymbol{\Delta}_\perp}) \right\rangle_\textrm{N}^2$.
• Figure 5: Ratio of the fraction of $q\bar{q}$ diffractive events in nuclei to the fraction in a proton plotted versus atomic number $A$ for fixed $x$ and $Q^2$ values.