Precision Dijet Acoplanarity Tomography of the Chromo Structure of Perfect QCD Fluids

TL;DR

This paper discusses how high-precision measurements of dijet acoplanarity in heavy-ion collisions can distinguish between different models of the quark-gluon plasma's chromo structure, specifically separating medium opacity and screening effects.

Contribution

It introduces a method to use acoplanarity distribution tails to separately constrain medium opacity and color screening scale in QCD fluids, comparing Gaussian and non-Gaussian broadening models.

Findings

High-precision measurements can identify non-Gaussian tails due to multiple collisions.

Sub-percent accuracy is needed to separately constrain medium parameters.

Current data constrains the saturation scale but not the individual medium properties.

Abstract

Dijet acoplanarity is dominated by vacuum (Sudakov) pQCD radiation even in Pb+Pb collisions, but future higher precision measurements of the tails of the acoplanarity distributions can help to resolve {\em separately} the medium opacity, $\chi=L/\lambda$, and the color screening scale $\mu^2$ from the path averaged BDMS saturation scale $Q_s^2[\chi,\mu]=\int dL\; \hat{q}(E,T(L))\propto \mu^2 L/\lambda $, that is already well constrained by nuclear modification factor data on $R_{AA}(p_T)$. We compare Gaussian (BDMS) and non-Gaussian (GLV) models of medium broadening of vacuum (Sudakov) induced acoplanarity distributions in A+A. With few percent accuracy on the ratio of A+A to p+p distributions, experiments can easily identify non-Gaussian Landau and Rutherford tails due to multiple collisions. However, we find that sub-percent precision will be required to constrain $\chi$ and $\mu$ separately from $Q_s$.