[Paper Review] Two-particle correlations with strange baryons and mesons at RHIC

J. Bielčíková|ArXiv.org|Jul 20, 2007

High-Energy Particle Collisions Research3 citations

TL;DR

This study investigates two-particle correlations involving strange baryons (Λ, Λ̄) and mesons (K⁰ₛ) at RHIC to disentangle jet-like and ridge-like correlations in d+Au and Au+Au collisions. Using identified particles at intermediate pT, it finds that the ridge yields exhibit enhanced baryon/meson ratios (Λ/K⁰ₛ ≈ 0.81 ± 0.14) compared to jets (0.46 ± 0.21), suggesting distinct particle production mechanisms for the ridge, with implications for parton recombination and medium-induced correlations in heavy-ion collisions.

ABSTRACT

We present results on two-particle correlations using singly-strange particles ($Λ$, $\barΛ$, $K^0_S$) and charged hadrons at intermediate p_T in d+Au and Au+Au collisions at RHIC. We discuss properties of the near-side correlation peak in both azimuthal and pseudo-rapidity space and separate jet-like contributions from the long-range pseudo-rapidity correlations (the ridge). In particular, we study the centrality and p_T dependence of the jet and ridge yields for various trigger and associated particle species and compare the results to model predictions.

Motivation & Objective

• To understand the origin of long-range near-side correlations (the ridge) in heavy-ion collisions by studying two-particle azimuthal and pseudo-rapidity correlations.
• To separate jet-like and ridge contributions in two-particle correlations using identified strange particles (Λ, Λ̄, K⁰ₛ) and charged hadrons.
• To investigate the centrality and pT dependence of jet and ridge yields across different particle species.
• To compare observed baryon/meson ratios in jet and ridge components with model predictions to constrain particle production mechanisms.
• To determine whether the ridge arises from thermal recombination, jet-medium interactions, or collective flow effects in the quark-gluon plasma.

Proposed method

• Measures two-particle correlation functions C(Δϕ) using data from the STAR experiment at √sNN = 200 GeV in d+Au and Au+Au collisions.
• Applies Gaussian fits to the near-side peak in azimuthal correlation functions, corrected for detector acceptance, efficiency, and TPC sector effects.
• Separates jet and ridge contributions by analyzing correlation yields in two Δη windows: |Δη| < 0.7 (jet + ridge) and |Δη| > 0.7 (ridge-only), assuming negligible jet yield at large Δη.
• Uses the jet yield in |Δη| < 0.7 as a baseline, with v₂-modulated background subtraction in Au+Au to isolate ridge contributions.
• Calculates baryon/meson ratios (Λ/K⁰ₛ) for both jet and ridge components using associated particle spectra in different pT ranges.
• Compares results to theoretical models such as parton recombination, jet quenching with radial flow, and color field instabilities in expanding media.

Experimental results

Research questions

• RQ1 How do jet-like and ridge-like correlations differ in strength and pT dependence for strange baryons and mesons?
• RQ2 What is the baryon/meson ratio in the ridge relative to the jet, and does it differ from that in p+p or d+Au collisions?
• RQ3 Does the ridge exhibit enhanced baryon production consistent with parton recombination models?
• RQ4 How does the inverse slope of the associated particle spectrum in the ridge compare to that of bulk thermal particles?
• RQ5 Which theoretical models—recombination, jet-medium interaction, or collective flow—best describe the observed ridge structure and composition?

Key findings

• The ridge contribution dominates the near-side correlation peak in central Au+Au collisions, with strength increasing steeply with centrality.
• The inverse slope of the associated particle spectrum in the ridge is approximately 50 MeV higher than that of bulk thermal particles.
• The baryon/meson ratio (Λ/K⁰ₛ) in the jet is 0.46 ± 0.21, consistent with p+p collisions and indicating minimal modification in the medium.
• The baryon/meson ratio in the ridge is 0.81 ± 0.14, significantly higher than in the jet, suggesting enhanced baryon production in ridge-associated particles.
• The ridge yield is independent of centrality within errors, contrasting with the increasing jet yield in peripheral collisions.
• The observed baryon enhancement in the ridge is inconsistent with models predicting only a 15 MeV higher inverse slope, indicating a need for refined theoretical frameworks.