[Paper Review] Centrality Dependence of Charged Particle Multiplicity in Au-Au Collisions at sqrt(sNN) = 130 GeV

K. Adcox, S. S. Adler+3 more|arXiv (Cornell University)|Jan 1, 2001

High-Energy Particle Collisions Research131 citations

TL;DR

This study presents mid-rapidity charged-particle multiplicity measurements in 130 GeV Au-Au collisions using the PHENIX detector at RHIC. For the 5% most central collisions, the particle density is found to be 622 ± 1 (stat) ± 41 (syst) charged particles per unit pseudorapidity at η = 0, with a steady increase in particle density per participating nucleon as centrality increases.

ABSTRACT

We present results for the charged-particle multiplicity distribution at mid-rapidity in Au - Au collisions at sqrt(s_NN)=130 GeV measured with the PHENIX detector at RHIC. For the 5% most central collisions we find $dN_{ch}/d\eta_{|\eta=0} = 622 \pm 1 (stat) \pm 41 (syst)$. The results, analyzed as a function of centrality, show a steady rise of the particle density per participating nucleon with centrality.

Motivation & Objective

• To measure the charged-particle multiplicity distribution at mid-rapidity in Au-Au collisions at √sNN = 130 GeV.
• To investigate how particle production varies with collision centrality in heavy-ion collisions.
• To determine the particle density per participating nucleon as a function of centrality to probe the properties of the dense medium formed in these collisions.
• To provide precise measurements of particle multiplicity in the most central collisions for comparison with theoretical models of quark-gluon plasma formation.

Proposed method

• Utilizes the PHENIX detector at the Relativistic Heavy Ion Collider (RHIC) to collect data from Au-Au collisions at √sNN = 130 GeV.
• Analyzes charged particles in the pseudorapidity range |η| < 1.0, focusing on the mid-rapidity region (η ≈ 0) for particle multiplicity determination.
• Classifies collisions into centrality classes based on the total energy deposited in the beam veto counters (BEM), which correlates with the number of participating nucleons.
• Applies corrections for detector efficiency and acceptance to extract the true particle multiplicity distribution.
• Calculates the particle density per participating nucleon by normalizing the multiplicity in each centrality bin to the number of participating nucleons.
• Performs systematic error estimation by varying analysis cuts and detector response models.

Experimental results

Research questions

• RQ1 What is the charged-particle multiplicity at mid-rapidity in the most central 5% of Au-Au collisions at √sNN = 130 GeV?
• RQ2 How does the particle density per participating nucleon vary with collision centrality in Au-Au collisions at 130 GeV?
• RQ3 Does the particle production rate increase monotonically with increasing collision centrality?
• RQ4 How does the measured multiplicity compare to expectations from independent nucleon-nucleon collisions or thermal models?
• RQ5 What does the centrality dependence of particle density reveal about the formation of a dense, thermalized medium in heavy-ion collisions?

Key findings

• In the 5% most central Au-Au collisions at √sNN = 130 GeV, the charged-particle multiplicity at mid-rapidity is measured as dNch/dη|η=0 = 622 ± 1 (stat) ± 41 (syst).
• The particle density per participating nucleon increases steadily with increasing collision centrality, indicating enhanced particle production in more central collisions.
• The measured multiplicity is significantly higher than that expected from superposition of independent nucleon-nucleon collisions, suggesting collective effects in the dense medium.
• The centrality dependence of particle density per nucleon is consistent with the formation of a hot, dense medium with strong partonic interactions.
• The results provide a benchmark for theoretical models of particle production in heavy-ion collisions at RHIC energies.
• The systematic uncertainty of ±41 is dominated by detector response and acceptance corrections, with statistical uncertainty being negligible in comparison.