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Formation of dense partonic matter in relativistic nucleus-nucleus collisions at RHIC: Experimental evaluation by the PHENIX collaboration

PHENIX Collaboration, K. Adcox

TL;DR

<3-5 sentence high-level summary>PHENIX presents a comprehensive RHIC-era analysis showing that Au+Au collisions produce matter with energy densities far above the QCD transition threshold and exhibit rapid thermalization and strong collective flow, inconsistent with ordinary hadronic matter. The work combines global observables, spectra, flow, correlations, fluctuations, and hard probes to infer an initial dense partonic medium and in-medium parton energy loss, consistent with a deconfined quark-gluon plasma in many but not all aspects. While hydrodynamic models capture several bulk features, tensions with HBT radii and some PID-dependent observables indicate a more nuanced space-time evolution and EOS, necessitating further theory and high-statistics, penetrating-probe measurements. Overall, the data provide compelling evidence for high-density, strongly interacting matter at RHIC, with direct photons and charm supports binary scaling in initial hard processes and jet quenching signaling a dense medium, culminating in a rich program to unravel the exact nature of the produced state.</paper_summary>

Abstract

Extensive experimental data from high-energy nucleus-nucleus collisions were recorded using the PHENIX detector at the Relativistic Heavy Ion Collider (RHIC). The comprehensive set of measurements from the first three years of RHIC operation includes charged particle multiplicities, transverse energy, yield ratios and spectra of identified hadrons in a wide range of transverse momenta (p_T), elliptic flow, two-particle correlations, non-statistical fluctuations, and suppression of particle production at high p_T. The results are examined with an emphasis on implications for the formation of a new state of dense matter. We find that the state of matter created at RHIC cannot be described in terms of ordinary color neutral hadrons.

Formation of dense partonic matter in relativistic nucleus-nucleus collisions at RHIC: Experimental evaluation by the PHENIX collaboration

TL;DR

<3-5 sentence high-level summary>PHENIX presents a comprehensive RHIC-era analysis showing that Au+Au collisions produce matter with energy densities far above the QCD transition threshold and exhibit rapid thermalization and strong collective flow, inconsistent with ordinary hadronic matter. The work combines global observables, spectra, flow, correlations, fluctuations, and hard probes to infer an initial dense partonic medium and in-medium parton energy loss, consistent with a deconfined quark-gluon plasma in many but not all aspects. While hydrodynamic models capture several bulk features, tensions with HBT radii and some PID-dependent observables indicate a more nuanced space-time evolution and EOS, necessitating further theory and high-statistics, penetrating-probe measurements. Overall, the data provide compelling evidence for high-density, strongly interacting matter at RHIC, with direct photons and charm supports binary scaling in initial hard processes and jet quenching signaling a dense medium, culminating in a rich program to unravel the exact nature of the produced state.</paper_summary>

Abstract

Extensive experimental data from high-energy nucleus-nucleus collisions were recorded using the PHENIX detector at the Relativistic Heavy Ion Collider (RHIC). The comprehensive set of measurements from the first three years of RHIC operation includes charged particle multiplicities, transverse energy, yield ratios and spectra of identified hadrons in a wide range of transverse momenta (p_T), elliptic flow, two-particle correlations, non-statistical fluctuations, and suppression of particle production at high p_T. The results are examined with an emphasis on implications for the formation of a new state of dense matter. We find that the state of matter created at RHIC cannot be described in terms of ordinary color neutral hadrons.

Paper Structure

This paper contains 53 sections, 33 equations, 56 figures, 1 table.

Table of Contents

  1. INTRODUCTION
  2. Historical Introduction
  3. Experimental Program
  4. Organization of this Document
  5. ENERGY DENSITY AND $E_T$, $N_{CH}$
  6. General Energy Density
  7. Formed Energy Density
  8. Realistic $\tau_{Form}$ and $\varepsilon_{Bj}$ estimates
  9. Thermalized Energy Density
  10. What Are the Initial Quanta?
  11. Conclusions
  12. THERMALIZATION
  13. Chemical Equilibrium
  14. Spectra
  15. Elliptic Flow
  16. ...and 38 more sections

Figures (56)

  • Figure 1: Lattice QCD results Karsch:2001cy for the energy density / $T^4$ as a function of the temperature scaled by the critical temperature $T_C$. Note the arrows on the right side indicating the values for the Stefan-Boltzmann limit.
  • Figure 2: Theoretical phase diagram of nuclear matter for two massless quarks as a function of temperature $T$ and baryon chemical potential $\mu$Rajagopal:2000uu.
  • Figure 3: Perturbative QCD results for the pressure as a function of temperature at various orders normalized to the Stefan-Boltzmann value $p_{SB}$Kajantie:2002wa.
  • Figure 4: Schematic drawing of the time and energy density scales derived through the Bjorken picture.
  • Figure 5: Figure from Bjorken Bjorken:1983qr illustrating the geometry of initially produced particles at a time $t$ after the overlap of the incoming nuclei in some frame. The picture is valid in any frame in which the incoming nuclei have very high energies and so are highly Lorentz contracted.
  • ...and 51 more figures