Logo
ScienceStack
Table of Contents
Fetching ...
Sign In

Hadron Emission and Stopping in Heavy-Ion Collisions: Baryon-Rich Matter to Meson-Dominated Matter

Manuel Lorenz, Christoph Blume

Abstract

Today's accelerator facilities used for studies of relativistic heavy-ion collisions cover an energy range spanning over three orders of magnitude, from a few GeV up to a few TeV in center-of-mass energy per nucleon pair ($\sqrt{s_{NN}}$). We present a systematic overview of hadron emission in heavy-ion collisions across this entire energy range. The presented energy excitation functions of the approximated baryon and meson yields at mid-rapidity reflect the interplay between baryon stopping and particle production, both of which evolve continuously with increasing energy. At low energies (e.g., SIS18, AGS), strong nuclear stopping leads to high net-baryon densities at mid-rapidity and to the abundant formation of nuclear clusters. With increasing $\sqrt{s_{NN}}$, the relative baryon stopping power $\langle δy \rangle / y_p$ decreases, and meson production becomes dominant. The inelasticity, i.e. the fraction of the initial kinetic energy available converted in inelastic reactions into particle production and dynamics, is found to rise rapidly at low energies and then levels off at values around $0.7 - 0.8$. While at low energies up to $\sim 10$~GeV this available energy seems to be shared by equal amount between the production of new particles and the dynamics of the system, as well as radiation, the latter part starts to dominates at higher energies.

Hadron Emission and Stopping in Heavy-Ion Collisions: Baryon-Rich Matter to Meson-Dominated Matter

Abstract

Today's accelerator facilities used for studies of relativistic heavy-ion collisions cover an energy range spanning over three orders of magnitude, from a few GeV up to a few TeV in center-of-mass energy per nucleon pair (). We present a systematic overview of hadron emission in heavy-ion collisions across this entire energy range. The presented energy excitation functions of the approximated baryon and meson yields at mid-rapidity reflect the interplay between baryon stopping and particle production, both of which evolve continuously with increasing energy. At low energies (e.g., SIS18, AGS), strong nuclear stopping leads to high net-baryon densities at mid-rapidity and to the abundant formation of nuclear clusters. With increasing , the relative baryon stopping power decreases, and meson production becomes dominant. The inelasticity, i.e. the fraction of the initial kinetic energy available converted in inelastic reactions into particle production and dynamics, is found to rise rapidly at low energies and then levels off at values around . While at low energies up to ~GeV this available energy seems to be shared by equal amount between the production of new particles and the dynamics of the system, as well as radiation, the latter part starts to dominates at higher energies.

Paper Structure

This paper contains 7 sections, 6 equations, 6 figures, 1 table.

Table of Contents

  1. The Landscape of Relativistic Heavy-Ion-Collisions
  2. General Characteristics of HICs
  3. Baryon Stopping
  4. Particle Production
  5. The transition from baryon- to meson dominated matter
  6. Quantitative relation of stopping and particle production
  7. Conclusions

Figures (6)

  • Figure S1: Rapidity distributions of net-baryons for central heavy-ion collisions at various collision energies E-802:1998xumNA49:1998gazBRAHMS:2003wwg as well as preliminary HADES data. With increasing energy, a valley in the yield distribution of net-baryons around mid-rapidity develops. Right: Energy excitation function of the $\pi^+$, proton and antiproton yields per average participating nucleon $A_{part}$ emitted at mid-rapidity in central Au+Au (Pb+Pb) collisions FOPI:2006ifgE-0895:2003oasNA49:2007stjNA49:2002pzuSTAR:2008medSTAR:2002hprSTAR:2017salALICE:2013mezFOPI:2010xrtBack:2002icE802:1999hit.
  • Figure S2: Energy excitations function of meson (blue triangles) and baryon (black dots) yields emitted at mid-rapidity in central Au+Au (Pb+Pb) collisions.
  • Figure S3: Left: the average rapidity loss $\langle\delta y\rangle$ of the net-baryons as a function of the center-of-mass energy $\sqrt{s_{NN}}$, as extracted from available measurements of net-baryon distributions E802:1999hitE917:2000sptVidebaek:1995mfBlume:2007kwNA49:1998gazNA49:2008ysvNA49:2010lhgBRAHMS:2009wlgBRAHMS:2003wwg. The hatched boxes depict the systematic uncertainties due to the extrapolations. Also shown as open gray symbols are predictions by the UrQMD model Petersen:2006mp. Right: the average rapidity loss of the net-baryons divided by the projectile rapidity $y_p$.
  • Figure S4: Left: the average energy per net-baryon $\langle E_{B- \bar{B}} \rangle$ as a function of the center-of-mass energy $\sqrt{s_{NN}}$Blume:2007kwNA49:1998gazNA49:2008ysvNA49:2010lhgBRAHMS:2009wlgBRAHMS:2003wwg for central Au+Au(Pb+Pb) collisions. In addition, also the value extracted by the NA35 collaboration for central S+S collisions at 200 $A$GeV is shown NA35:1994adm. The data points are fitted with a function $f = a \cdot \sqrt{s_{NN}} + b$, yielding the parameters $a = 0.13 \pm 0.01$ and $b = 0.81 \pm 0.03$ GeV. Right: the average inelastic energy per net-baryon $\langle E_{inel} \rangle$. Also shown as gray symbols is an estimate on the amount of inelastic energy used for the creation of hadronic mass, calculated for mesons (open crosses), baryons (open stars) and their sum (hadrons, filled crosses), see text for details.
  • Figure S5: Left: the total inelasticity $K_{total}$ as a function of the center-of-mass energy $\sqrt{s_{NN}}$ (colored, filled symbols). The fraction $K_{mass}$ that is used for hadronic mass generation is also shown as gray symbols for mesons (open crosses), baryons (open stars) and their sum (hadrons, filled crosses). Right: the fraction of the inelasticity going into the dynamics of newly produced particles and into radiation $K_{dyn+rad}$. The data points are fitted with a function $f = a \cdot \ln^b(\sqrt{s_{NN}} / (2 \, m_p))$, yielding the parameters $a = 0.28 \pm 0.02$ and $b = 0.52 \pm 0.09$.
  • ...and 1 more figures