Dihadron azimuthal correlations in Au+Au collisions at sqrt(s_NN)=200 GeV

TL;DR

The paper provides a comprehensive, differential study of dihadron azimuthal correlations in Au+Au collisions at 200 GeV, decomposing jet-induced signals from an elliptic-flow background. It reveals a four-component picture of jet modification: near-side fragmentation, away-side fragmentation (punch-through), and two medium-induced responses that populate low-to-intermediate pT, with energy redistributed to soft hadrons and a notable ridge/shoulder structure. By mapping pT and centrality dependencies, the work constrains jet quenching dynamics and medium response, offering insights into transport properties and the interplay between hard and soft processes in the quark-gluon plasma. The results are broadly consistent with Mach-cone-like hydrodynamic responses and energy-loss scenarios that couple jet quenching to medium excitations, while also highlighting areas where models require further development to capture the full Δφ–Δη landscape. Overall, it provides a robust, data-driven framework for disentangling fragmentation from medium-induced phenomena in heavy-ion jet correlations.

Abstract

Azimuthal angle (Delta phi) correlations are presented for a broad range of transverse momentum (0.4 < pT < 10 GeV/c) and centrality (0-92%) selections for charged hadrons from di-jets in Au+Au collisions at sqrt(s_NN) = 200 GeV. With increasing pT, the away-side Delta phi distribution evolves from a broad and relatively flat shape to a concave shape, then to a convex shape. Comparisons to p+p data suggest that the away-side distribution can be divided into a partially suppressed head region centered at Delta phi ~ π, and an enhanced shoulder region centered at Delta phi ~ π\pm 1:1. The pT spectrum for the associated hadrons in the head region softens toward central collisions. The spectral slope for the shoulder region is independent of centrality and trigger pT . The properties of the near-side distributions are also modified relative to those in p + p collisions, reflected by the broadening of the jet shape in Delta phi and Delta eta, and an enhancement of the per-trigger yield. However, these modifications seem to be limited to pT < 4 GeV/c, above which both the dihadron pair shape and per-trigger yield become similar to p + p collisions. These observations suggest that both the away- and near-side distributions contain a jet fragmentation component which dominates for pT \ge 5GeV and a medium-induced component which is important for pT \le 4 GeV/c. We also quantify the role of jets at intermediate and low pT through the yield of jet-induced pairs in comparison to binary scaled p + p pair yield. The yield of jet-induced pairs is suppressed at high pair proxy energy (sum of the pT magnitudes of the two hadrons) and is enhanced at low pair proxy energy. The former is consistent with jet quenching; the latter is consistent with the enhancement of soft hadron pairs due to transport of lost energy to lower pT.

Figures (38)

• Figure 1: (Color online) Cartoon of hadron pair distribution in $\Delta\phi$ for $p+p$ collisions. It has two peaks corresponding to near- and away-side jet, and a flat component representing the underlying event pairs.
• Figure 2: (Color online) The correlation function for $2<p_{\rm T}^{\rm a}<3$, $1<p_{\rm T}^{\rm b}<2$ GeV/$c$ in 0-5% Au+Au collisions. The dashed line represents the estimated elliptic flow modulated combinatoric background using zero yield at minimum (ZYAM) method (see Section.\ref{['sec:3.4']}).
• Figure 3: (Color online) The $p+p$ jet-induced hadron-pair yield $\Delta\phi$ distributions calculated from the per-trigger yield using low-$p_\mathrm{T}\,$ hadrons as triggers (solid symbols) and high-$p_\mathrm{T}\,$ hadrons as triggers (open symbols).
• Figure 4: (Color online) The 0-20% Au+Au jet-induced hadron-pair yield $\Delta\phi$ distributions calculated from the per-trigger yield using low-$p_\mathrm{T}\,$ hadrons as triggers (solid symbols) and high-$p_\mathrm{T}\,$ hadrons as triggers (open symbols).
• Figure 5: (Color online) PYTHIA simulation showing jet-induced hadron pair $\Delta\phi$ distribution for $3<p_{T}^{\rm a}, p_{\rm T}^{\rm b}<5$ GeV/$c$ with (top histogram) and without (bottom histogram) initial and final state radiation. The radiation accounts for the increase of the background level.