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Nuclear cluster structure effect in $^{16}$O+$^{16}$O collisions at the top RHIC energy

Xin-Li Zhao, You Zhou, Zi-Wei Lin, Chao Zhang, Guo-Liang Ma

TL;DR

This work investigates whether nuclear-structure effects, notably $\alpha$-clustering in $^{16}$O, imprint on relativistic O+O collisions at $\sqrt{s_{NN}}=200$ GeV. Using an improved AMPT-SM transport framework, the authors implement four $^{16}$O configurations (Woods-Saxon, tetrahedron, square, NLEFT) and quantify initial geometry with the cumulant ratio $\varepsilon_2\{4\}/\varepsilon_2\{2\}$, then compare azimuthal anisotropy observables $v_2$ and $v_3$ to STAR data under STAR-like non-flow subtraction. They adjust the hadron formation time to control early hadronic energy density, enabling reasonable centrality trends and achieving good agreement for $v_2(p_T)$ at low $p_T$ and $v_3(p_T)$ over the full range, as well as for integrated $v_2\{2\}$ and $v_3\{2\}$. The findings indicate that nuclear geometry can significantly influence flow in intermediate-size systems and that a unified transport model can serve as a baseline for probing clustering across energies and differential observables.

Abstract

Using the improved AMPT-SM model, we investigated the impact of nuclear geometry of $^{16}$O on anisotropic flows in O+O collisions at $\sqrt{s_{_{\mathrm{NN}}}}=200$ GeV. To evaluate the influence of nuclear structure and potential alpha clustering, we implemented four candidate configurations: Woods-Saxon, tetrahedron, square, and NLEFT. Initial-state geometry is quantified via the eccentricity cumulant ratio $\varepsilon_{2}\{4\}/\varepsilon_{2}\{2\}$, which provides a robust and evolution-independent measure sensitive to configuration differences. The model reproduces $v_{2}(p_{\mathrm{T}})$ at low $p_{\mathrm{T}}$ and $v_{3}(p_{\mathrm{T}})$ across the full $p_{\mathrm{T}}$ range, with integrated $v_{2}\{2\}$ and $v_{3}\{2\}$ matching the STAR data, demonstrating that transport dynamics captures the essential collectivity in this intermediate-size system. These findings establish a baseline for extending nuclear-structure studies in O+O collisions to other energies and differential observables within a unified transport model framework.

Nuclear cluster structure effect in $^{16}$O+$^{16}$O collisions at the top RHIC energy

TL;DR

This work investigates whether nuclear-structure effects, notably -clustering in O, imprint on relativistic O+O collisions at GeV. Using an improved AMPT-SM transport framework, the authors implement four O configurations (Woods-Saxon, tetrahedron, square, NLEFT) and quantify initial geometry with the cumulant ratio , then compare azimuthal anisotropy observables and to STAR data under STAR-like non-flow subtraction. They adjust the hadron formation time to control early hadronic energy density, enabling reasonable centrality trends and achieving good agreement for at low and over the full range, as well as for integrated and . The findings indicate that nuclear geometry can significantly influence flow in intermediate-size systems and that a unified transport model can serve as a baseline for probing clustering across energies and differential observables.

Abstract

Using the improved AMPT-SM model, we investigated the impact of nuclear geometry of O on anisotropic flows in O+O collisions at GeV. To evaluate the influence of nuclear structure and potential alpha clustering, we implemented four candidate configurations: Woods-Saxon, tetrahedron, square, and NLEFT. Initial-state geometry is quantified via the eccentricity cumulant ratio , which provides a robust and evolution-independent measure sensitive to configuration differences. The model reproduces at low and across the full range, with integrated and matching the STAR data, demonstrating that transport dynamics captures the essential collectivity in this intermediate-size system. These findings establish a baseline for extending nuclear-structure studies in O+O collisions to other energies and differential observables within a unified transport model framework.
Paper Structure (8 sections, 7 equations, 18 figures)

This paper contains 8 sections, 7 equations, 18 figures.

Table of Contents

  1. Introduction
  2. Geometry configurations and improved AMPT model
  3. Observables and methodology
  4. Results and discussions
  5. Conclusion
  6. Delay of hadron cascade in the AMPT-SM model
  7. Different methods for non-flow subtraction
  8. $\left<p_{\rm T} \right>$ results for O+O collisions

Figures (18)

  • Figure 1: Illustration of the geometrical configuration of $^{16}$O with the nucleon structures of (a) W-S distribution, (b) tetrahedron distribution, and (c) square distribution.
  • Figure 2: The nucleon density distribution inside $^{16}$O in O+O collisions with the geometrical configurations of W-S, tetrahedron, square, and NLEFT distributions.
  • Figure 3: The centrality dependence of $\left<p_{\rm T} \right>$ in O+O collisions at 200 GeV with the tetrahedron configuration of nuclear structure for two versions of the AMPT model with parton cross section 1.5 mb.
  • Figure 4: The centrality dependence of $v_{2}\{2\}$ in O+O collisions at 200 GeV with different settings in the improved AMPT model for the tetrahedron configuration.
  • Figure 5: The centrality dependence of (a) $\varepsilon_2$ and (b) $\varepsilon_3$ in O+O collisions at 200 GeV with different nuclear structure configurations.
  • ...and 13 more figures