Identified charged hadron production in Au+Au collisions at $\sqrt{s_\mathrm{NN}}$ = 54.4 GeV with the STAR detector

TL;DR

This study measures identified charged-hadron (π^{±}, K^{±}, p, bar{p}) production at mid-rapidity in Au+Au collisions at √s_NN = 54.4 GeV with the STAR detector. By analyzing transverse-momentum spectra across nine centrality classes, it extracts bulk observables dN/dy, ⟨p_T⟩, particle ratios, and kinetic freeze-out parameters T_{kin} and ⟨β_T⟩ using blast-wave fits, as well as the Bjorken energy density product ε_{BJ} × τ. The results reveal mass-dependent spectral shapes and centrality trends consistent with radial flow, along with antiparticle–particle ratios approaching unity for pions and showing energy-dependent behavior for kaons and protons. Comparisons to AMPT and HIJING highlight strengths and limitations of current heavy-ion collision models in reproducing yields, mean transverse momenta, and energy-density scaling, offering constraints on the interplay between initial conditions and medium evolution. The observed ε_{BJ} × τ values exceed lattice-predicted phase-transition thresholds, indicating high initial energy density at formation time across energies and system sizes studied.

Abstract

We present results on the production of $π^{\pm}$, $K^{\pm}$, $p$, and $\bar{p}$ in Au+Au collisions at $\sqrt{s_\mathrm{NN}}$ = 54.4 GeV using the STAR detector at RHIC, at mid-rapidity ($|y| <$ 0.1). Invariant yields of these particles as a function of transverse momentum are shown. We determine bulk properties such as integrated particle yields ($dN/dy$), mean transverse momentum ($\langle p_{T} \rangle$), particle ratios, which provide insight into the particle production mechanisms. Additionally, the kinetic freeze-out parameters ($T_\text{kin}$ and $\langle β_{T} \rangle$), which provide information about the dynamics of the system at the time of freeze-out, are obtained. The Bjorken energy density ($ε_{BJ}$), which gives an estimate of the energy density in the central rapidity region of the collision zone at the formation time $τ$, is calculated and presented as a function of multiplicity for various energies. The results are compared with those from the models such as A Multi-Phase Transport (AMPT) and Heavy Ion Jet INteraction Generator (HIJING) for further insights.

Figures (16)

• Figure 1: The transverse momentum spectra for (a) $\pi^{+}$, (b) $K^{+}$, (c) $p$, (d) $\pi^{-}$, (e) $K^{-}$ and (f) $\bar{p}$ at mid-rapidity ($|y| < 0.1$) in Au+Au collisions at $\sqrt{s_\mathrm{NN}}$ = 54.4 GeV for nine centrality classes. The spectra for all the centralities other than 0-5% are scaled for clarity. The curves represent the Bose-Einstein functional fit to pions, Levy-Tsallis fit to kaons, and double-exponential fit to protons and anti-protons for 0-5% centrality. The statistical and systematic uncertainties are added in quadrature.
• Figure 2: The $\langle \rm{N_{part}}\rangle$ dependence of the normalized integrated particle yield ($dN/dy/(\langle \rm{N_{part}}\rangle/2$) for (a) $\pi^{+}$, (b) $K^{+}$, (c) $p$, (d) $\pi^{-}$, (e) $K^{-}$, (f) $\bar{p}$ at mid-rapidity ($|y| < 0.1$) in Au+Au collisions at $\sqrt{s_\mathrm{NN}}$ = 54.4 GeV. The results are compared with the published results at other STAR energies BESSTAR:2008med. The statistical and systematic uncertainties are added in quadrature where the latter dominates. $\rm \langle N_{part}\rangle$ uncertainties are not combined in quadrature for clarity of plots.
• Figure 3: The $\langle \rm{N_{part}}\rangle$ dependence of mean transverse momentum ($\langle p_{T} \rangle$) of (a) $\pi^{+}$, (b) $K^{+}$, (c) $p$, (d) $\pi^{-}$, (e) $K^{-}$, (f) $\bar{p}$ at mid-rapidity ($|y| < 0.1$) in Au+Au collisions at $\sqrt{s_\mathrm{NN}}$ = 54.4 GeV. The results are compared with the published results at other STAR energies BESSTAR:2008med. The statistical and systematic uncertainties are added in quadrature where the latter dominates.
• Figure 4: The $\langle \rm{N_{part}}\rangle$ dependence of the antiparticle to particle ratios (a) $\pi^{-}$/$\pi^{+}$, (b) $K^{-}$/$K^{+}$ and (c) $\bar{p}$/$p$ at mid-rapidity ($|y| <$ 0.1) in Au+Au collisions at $\sqrt{s_\mathrm{NN}}$ = 54.4 GeV. The results are compared with the published results at other STAR energies BESSTAR:2008med. The statistical and systematic uncertainties are added in quadrature where the latter dominates.
• Figure 5: The $\langle \rm{N_{part}}\rangle$ dependence of mixed ratios (a) $K^{+}$/$\pi^{+}$, (b) ${p}$/$\pi^{+}$, (c) $K^{-}$/$\pi^{-}$ and (d) $\bar{p}$/$\pi^{+}$ at mid-rapidity ($|y| <$ 0.1) in Au+Au collisions at $\sqrt{s_\mathrm{NN}}$ = 54.4 GeV. The results are compared with the published results at other STAR energies BESSTAR:2008med. The statistical and systematic uncertainties are added in quadrature where the latter dominates.