Quadrupole Anisotropy in Dihadron Azimuthal Correlations in Central $d$$+$Au Collisions at $\sqrt{s_{_{NN}}}$=200 GeV

TL;DR

This paper reports measurements of azimuthal dihadron correlations in central $d$+Au collisions at 200 GeV, revealing quadrupole anisotropy similar to LHC results, supporting hydrodynamic flow as a possible origin.

Contribution

It provides the first detailed comparison of azimuthal anisotropies in $d$+Au collisions at RHIC with those in $p$+Pb collisions at the LHC, highlighting the role of initial-state eccentricity.

Findings

Larger anisotropies in $d$+Au than in $p$+Pb collisions.

Scaled anisotropies follow a common trend with multiplicity.

Results are consistent with hydrodynamic flow explanations.

Abstract

The PHENIX collaboration at the Relativistic Heavy Ion Collider (RHIC) reports measurements of azimuthal dihadron correlations near midrapidity in $d$$+$Au collisions at $\sqrt{s_{_{NN}}}$=200 GeV. These measurements complement recent analyses by experiments at the Large Hadron Collider (LHC) involving central $p$$+$Pb collisions at $\sqrt{s_{_{NN}}}$=5.02 TeV, which have indicated strong anisotropic long-range correlations in angular distributions of hadron pairs. The origin of these anisotropies is currently unknown. Various competing explanations include parton saturation and hydrodynamic flow. We observe qualitatively similar, but larger, anisotropies in $d$$+$Au collisions compared to those seen in $p$$+$Pb collisions at the LHC. The larger extracted $v_2$ values in $d$$+$Au collisions at RHIC are consistent with expectations from hydrodynamic calculations owing to the larger expected initial-state eccentricity compared with that from $p$$+$Pb collisions. When both are divided by an estimate of the initial-state eccentricity the scaled anisotropies follow a common trend with multiplicity that may extend to heavy ion data at RHIC and the LHC, where the anisotropies are widely thought to arise from hydrodynamic flow.