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Strange Hadron Production at High Baryon Density

Hongcan Li

TL;DR

This work addresses how strange hadron production reveals the properties of QCD matter at high baryon density in Au+Au collisions. It employs STAR BES-II FXT data to measure $p_T$ spectra and $dN/dy$ for $K^0_S$, $\Lambda$, and $\Xi^-$, construct the strangeness excitation function, and analyze centrality scaling via $\alpha_S$, with comparisons to UrQMD. The key findings show yields increasing with collision energy, threshold-crossing behavior for multi-strange hadrons, and a decreasing centrality dependence as energy grows, constraining the high-baryon-density EoS and hadronization dynamics. Transport-model tensions at selected energies, especially for $\Xi^-$, point to missing medium effects in current descriptions. Overall, the study strengthens the role of strangeness as a diagnostic of QCD matter near the baryon-rich regime and informs the QCD phase diagram at high baryon density.

Abstract

Strange hadrons have been suggested as sensitive probes of the properties of the nuclear matter created in heavy-ion collisions. At few-GeV collision energies, the formed medium is baryon-rich due to baryon stopping effect. In these proceedings, the recent results on strange hadron production in Au+Au collisions at $\sqrt{s_{\rm{NN}}}$ = 3.2, 3.5, 3.9 and 4.5 GeV with the fixed-target mode from the STAR Beam Energy Scan phase-II program are presented. The transverse momentum spectra, rapidity density distributions, excitation function and centrality dependence of strange hadrons ($\rm{K}^0_S,~Λ, ~Ξ^-$) are shown. These results are compared with those from higher collision energies and physics implications are discussed by comparing to the transport model calculations.

Strange Hadron Production at High Baryon Density

TL;DR

This work addresses how strange hadron production reveals the properties of QCD matter at high baryon density in Au+Au collisions. It employs STAR BES-II FXT data to measure spectra and for , , and , construct the strangeness excitation function, and analyze centrality scaling via , with comparisons to UrQMD. The key findings show yields increasing with collision energy, threshold-crossing behavior for multi-strange hadrons, and a decreasing centrality dependence as energy grows, constraining the high-baryon-density EoS and hadronization dynamics. Transport-model tensions at selected energies, especially for , point to missing medium effects in current descriptions. Overall, the study strengthens the role of strangeness as a diagnostic of QCD matter near the baryon-rich regime and informs the QCD phase diagram at high baryon density.

Abstract

Strange hadrons have been suggested as sensitive probes of the properties of the nuclear matter created in heavy-ion collisions. At few-GeV collision energies, the formed medium is baryon-rich due to baryon stopping effect. In these proceedings, the recent results on strange hadron production in Au+Au collisions at = 3.2, 3.5, 3.9 and 4.5 GeV with the fixed-target mode from the STAR Beam Energy Scan phase-II program are presented. The transverse momentum spectra, rapidity density distributions, excitation function and centrality dependence of strange hadrons () are shown. These results are compared with those from higher collision energies and physics implications are discussed by comparing to the transport model calculations.
Paper Structure (7 sections, 4 figures)

This paper contains 7 sections, 4 figures.

Table of Contents

  1. Introduction
  2. Experimental and data analysis
  3. Results and discussions
  4. Transverse momentum spectra and rapidity density distribution
  5. Strangeness excitation function
  6. Scaling property of centrality dependence
  7. Summary

Figures (4)

  • Figure 1: Transverse momentum spectra of $\rm{K}^0_S, \Lambda$ and $\Xi^-$ in Au+Au central collision (0-10%) at $\sqrt{s_{\rm{NN}}}$ = 3.2, 3.5, 3.9 and 4.5 GeV. The black solid circles is the measured data points. Dash lines correspond to blast-wave or $m_{\rm T}$-exponential fits.
  • Figure 2: Rapidity distribution of $\rm{K}^0_S, \Lambda$ and $\Xi^-$ in Au+Au central collisions (0-10%) at $\sqrt{s_{\rm{NN}}}$ = 3.2, 3.5, 3.9 and 4.5 GeV. The vertical line is the statistical uncertainties, and the box is the systematic uncertainties.
  • Figure 3: Excitation function of $\rm{K}^0_S, \Lambda$ and $\Xi^-$ in Au+Au the most central collision. The solid points is STAR BES-II FXT-mode results and the open points is STAR BES-I and HADES resultsref-4ref-5ref-6ref-7. The NN collision threshold energies of $\Lambda$ and $\Xi^-$ are marked by two arrows.
  • Figure 4: Scaling parameter $\alpha_{\rm S}$ of $\rm{K}^0_S$, $\Lambda$ and $\Xi^-$ as a function of collision energy. Results from the transport model UrQMD is show as gray lines.