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Imaging shapes of ground-state uranium-238 nuclei in high-energy nuclear collisions at RHIC

Chunjian Zhang

TL;DR

The paper addresses how the shape and orientation of colliding nuclei influence the initial geometry of the quark-gluon plasma (QGP) and its final-state observables. It introduces a flow-assisted imaging method that maps nuclear deformation parameters, notably the quadrupole beta-2 and triaxial gamma, to- and constrains them through a set of correlations among $v_2$, $p_T$ fluctuations, and their cross-terms, using deformed Woods-Saxon densities. The analysis of $^{238}$U+$^{238}$U versus $^{197}$Au+$^{197}$Au collisions yields a large quadrupole deformation with a small nonzero triaxiality, quantified as $\beta_{2,\mathrm{U}} \approx 0.29$ and $\gamma_{\mathrm{U}} \approx 8.7^{\circ}$, consistent with low-energy nuclear-structure data and providing new constraints on QGP initial conditions. This approach offers a general framework to image nuclear shapes across species and energy scales, linking high-energy collision observables to intrinsic nuclear structure.

Abstract

The shape and orientation of colliding nuclei play a crucial role in determining the initial conditions of the quark-gluon plasma (QGP), which influence key observables such as anisotropic and radial flow. In these proceedings, we present the measurements of $v_2$, $p_{\rm T}$ fluctuations and $v_2-p_{\rm T}$ correlations in $^{238}$U + $^{238}$U and $^{197}$Au + $^{197}$Au collisions at center of mass energies $\sqrt{s_{\rm NN}}=$ 193 and 200 GeV, respectively. Our results reveal significant differences in these observables between the two systems, particularly in the most central collisions. Comparisons with hydrodynamic model calculations indicate a large deformation in the ground states of $^{238}$U nuclei, consistent with previous low-energy experiments. However, data also imply a small deviation from axial symmetry of $^{238}$U [1]. Our work introduces a novel approach for imaging nuclear shapes, enhances the modeling of QGP initial conditions, and sheds light on nuclear structure evolution across different energy scales. The potential applications of this method for other nuclear species are discussed.

Imaging shapes of ground-state uranium-238 nuclei in high-energy nuclear collisions at RHIC

TL;DR

The paper addresses how the shape and orientation of colliding nuclei influence the initial geometry of the quark-gluon plasma (QGP) and its final-state observables. It introduces a flow-assisted imaging method that maps nuclear deformation parameters, notably the quadrupole beta-2 and triaxial gamma, to- and constrains them through a set of correlations among , fluctuations, and their cross-terms, using deformed Woods-Saxon densities. The analysis of U+U versus Au+Au collisions yields a large quadrupole deformation with a small nonzero triaxiality, quantified as and , consistent with low-energy nuclear-structure data and providing new constraints on QGP initial conditions. This approach offers a general framework to image nuclear shapes across species and energy scales, linking high-energy collision observables to intrinsic nuclear structure.

Abstract

The shape and orientation of colliding nuclei play a crucial role in determining the initial conditions of the quark-gluon plasma (QGP), which influence key observables such as anisotropic and radial flow. In these proceedings, we present the measurements of , fluctuations and correlations in U + U and Au + Au collisions at center of mass energies 193 and 200 GeV, respectively. Our results reveal significant differences in these observables between the two systems, particularly in the most central collisions. Comparisons with hydrodynamic model calculations indicate a large deformation in the ground states of U nuclei, consistent with previous low-energy experiments. However, data also imply a small deviation from axial symmetry of U [1]. Our work introduces a novel approach for imaging nuclear shapes, enhances the modeling of QGP initial conditions, and sheds light on nuclear structure evolution across different energy scales. The potential applications of this method for other nuclear species are discussed.

Paper Structure

This paper contains 4 sections, 1 equation, 2 figures.

Table of Contents

  1. Introduction
  2. Flow-assisted nuclear imaging method
  3. Accessing and constraining the $\beta_{\rm 2,U}$ and $\gamma_{\rm U}$ parameters
  4. Summary and applications

Figures (2)

  • Figure 1: $\langle v_2^2 \rangle$ verse $\delta p_{\rm T}/\langle[p_{\rm T}] \rangle$ in 0-0.5% most central $^{238}$U+$^{238}$U and $^{197}$Au+$^{197}$Au collisions in $0.2 < p_{\rm T} < 3$ GeV/$c$ at $\sqrt{s_{\rm NN}}=$ 193 GeV and 200 GeV, respectively. The head-on body-body and tip-tip configurations are illustrated.
  • Figure 2: Ratios of $\langle v_2^2 \rangle$, $\langle (\delta p_{\rm T})^2\rangle$, and $\langle v_2^2\delta p_{\rm T}\rangle$ in panels a-c between $^{238}$U+$^{238}$U and $^{197}$Au+$^{197}$Au collisions as a function of centrality compared with the hydrodynamic model. The data ratio values in 0-5% most central collisions are compared with hydrodynamic calculations for different $\beta_{2}$ and $\gamma$ scan in panels d-f. Panel g shows the constraint ranges of ($\beta_{2},\gamma)$ from these three observables separately and the confidence contours obtained by combining $\langle (\delta p_{\rm T})^2\rangle$ and $\langle v_2^2\delta p_{\rm T}\rangle$.