Probing Gluon Saturation through Dihadron Correlations at an Electron-Ion Collider

TL;DR

This paper assesses how dihadron azimuthal correlations in electron-proton and electron-ion DIS at a future Electron-Ion Collider can probe gluon saturation. Utilizing the saturation/CGC formalism, it links back-to-back dihadron production to the Weizsäcker-Williams gluon distribution, incorporating Sudakov resummation and modeling via GBW-like UGDs. Through EIC-relevant simulations (PYTHIA-based) of e+p and e+A with detector and beam configurations, the authors show a robust away-side suppression in e+A as a signature of saturation, distinguishable from nuclear PDF effects and parton showers. The work demonstrates the feasibility and physics impact of measuring dihadron correlations at the EIC, including direct access to WW UGDs and a test of saturation dynamics in small-x QCD.

Abstract

Two-particle azimuthal angle correlations have been proposed to be one of the most direct and sensitive probes to access the underlying gluon dynamics involved in hard scatterings. In anticipation of an Electron-Ion Collider (EIC), detailed studies of dihadron correlation measurements in electron-proton and electron-ion collisions at an EIC have been performed. The impact of such measurements on the understanding of the different gluon distribution functions, as a clean signature for gluon saturation and to constrain saturation models further, has been explored. It is shown that dihadron correlation measurements will be one of the key methods to probe gluon saturation phenomena at a future EIC.

Figures (13)

• Figure 1: [color online] $\pi^0$-correlation curves calculated in the saturation formalism at 10 GeV$\times$100 GeV for $e+p$ (thick line) and $e+$Au (thin line) with (dashed curve) and without (solid curve) the Sudakov factor. The kinematics chosen are $y=0.7$, $Q^2=1 \, \textrm{GeV}^2$, $z_{h1}=z_{h2}=0.3$, $p_{h1\perp}>2 \, \mathrm{GeV}/c,1 \, \mathrm{GeV}/c<p_{h2\perp}<p_{h1\perp}$.
• Figure 2: [color online] The eRHIC kinematics coverage compared to $p+$A at RHIC. The dash-dotted and dashed lines show the eRHIC kinematics for the beam energies of 10 GeV $\times$100 GeV and 20 GeV $\times$100 GeV, respectively. The solid lines represent the RHIC coverage at $\sqrt{s}=200$ GeV for $\eta=0$ and $\eta=4$, where $\eta=-\ln\tan(\theta/2)$ is the pseudorapidity of the particles.
• Figure 3: [color online] Expected yields of charged particle pairs at transverse momentum $p_{T}>1$ GeV/$c$ in bins of ($Q^{2}$, $x_{Bj}$) for an integrated luminosity of $1 \, fb^{-1}$ for $e+p$ 10 GeV $\times$100 GeV (Left) and 20 GeV $\times$100 GeV (Right) in the kinematic range of $1\, \textrm{GeV}^{2}<Q^{2}<20 \, \textrm{GeV}^{2}$, and $0.01<y<0.95$.
• Figure 4: [color online] Particle $p_{T}$ distributions for $e+p$ 10 GeV $\times$ 100 GeV collisions with $1 \, \mathrm{GeV}^{2} < Q^{2} < 20 \, \mathrm{GeV^{2}}, 0.01 < y < 0.95$. Left: charged particle production from LO DIS, gluon dijets (PGF and resolved gluon channel) and quark dijets (QCDC and resolved quark channel). Right: $\pi^{\pm}, K^{\pm}, p^{\pm}$ and $\pi^{0}$ production for all processes.
• Figure 5: Feynman diagrams for different PYTHIA subprocesses contributing to the hard interaction: (a) direct, (b) VMD, (c) anomalous. The dotted lines indicate the presence of a spectator. Bubbles stand for a hadron or hadronic structure.