Global analysis of color fluctuation effects in proton- and deuteron-nucleus collisions at RHIC and the LHC

TL;DR

This study analyzes how the interaction strength of protons with large-$x$ partons varies with energy in nuclear collisions, revealing a faster increase at higher energies and implications for the EMC effect.

Contribution

It provides the first quantitative extraction of the $x_p$-dependent interaction strength across RHIC and LHC energies using a global jet data analysis.

Findings

Interaction strength for small configurations grows faster with energy.

Large-$x_p$ configurations interact more weakly at lower energies.

Results support color screening explanations of the EMC effect.

Abstract

We test the hypothesis that configurations of a proton with a large-$x$ parton, $x_p \gtrsim 0.1$, have a smaller than average size. The QCD $Q^2$ evolution equations suggest that these small configurations also have a significantly smaller interaction strength, which has observable consequences in collisions with nuclei. We perform a global analysis of jet production data in proton- and deuteron-nucleus collisions at RHIC and the LHC. Using a model which takes a distribution of interaction strengths into account, we quantitatively extract the $x_p$-dependence of the average interaction strength, $\sigma(x_p)$, over a wide kinematic range. By comparing the RHIC and LHC results, our analysis finds that the interaction strength for small configurations, while suppressed, grows faster with collision energy than does that for average configurations. We check that this energy dependence is consistent with the results of a method which, given $\sigma(x_p)$ at one energy, can be used to quantitatively predict that at another. This finding further suggests that at even lower energies, nucleons with a large-$x_p$ parton should interact much more weakly than those in an average configuration, a phenomenon in line with explanations of the EMC effect for large-$x_p$ quarks in nuclei based on color screening.