Measurement of long-range angular correlation and quadrupole anisotropy of pions and (anti)protons in central $d$$+$Au collisions at $\sqrt{s_{_{NN}}}$=200 GeV

TL;DR

This study measures azimuthal correlations and anisotropy parameters in $d$+Au collisions at 200 GeV, revealing mass-dependent flow patterns similar to heavy ion collisions, and compares results with hydrodynamic models and $p$+Pb data.

Contribution

It provides the first detailed measurement of $v_2$ and mass-ordering in $d$+Au collisions at RHIC energies, extending understanding of collective effects in small systems.

Findings

Enhanced near-side correlations at large $ riangle ext{eta}$ in $d$+Au.

Mass-ordering pattern of $v_2$ similar to heavy ion collisions.

Smaller mass-ordering magnitude compared to $p$+Pb, indicating less radial flow.

Abstract

We present azimuthal angular correlations between charged hadrons and energy deposited in calorimeter towers in central $d$$+$Au and minimum bias $p$$+$$p$ collisions at $\sqrt{s_{_{NN}}}=200$ GeV. The charged hadron is measured at midrapidity $|\eta|<0.35$, and the energy is measured at large rapidity ($-3.7<\eta<-3.1$, Au-going direction). An enhanced near-side angular correlation across $|\Delta\eta| >$ 2.75 is observed in $d$$+$Au collisions. Using the event plane method applied to the Au-going energy distribution, we extract the anisotropy strength $v_2$ for inclusive charged hadrons at midrapidity up to $p_T=4.5$ GeV/$c$. We also present the measurement of $v_2$ for identified $\pi^{\pm}$ and (anti)protons in central $d$$+$Au collisions, and observe a mass-ordering pattern similar to that seen in heavy ion collisions. These results are compared with viscous hydrodynamic calculations and measurements from $p$$+$Pb at $\sqrt{s_{_{NN}}}=5.02$ TeV. The magnitude of the mass-ordering in $d$$+$Au is found to be smaller than that in $p$$+$Pb collisions, which may indicate smaller radial flow in lower energy $d$$+$Au collisions.