Exploring nuclear structure with multiparticle azimuthal correlations at the LHC

TL;DR

This study demonstrates that multiparticle azimuthal correlations in ultra-relativistic Xe–Xe and Pb–Pb collisions at the LHC can image nuclear structure parameters. By measuring a broad set of flow observables, including $v_n$, flow fluctuations, nonlinear flow modes ($v_{4,22}$), and symmetry-plane correlations ($\rho_{4,22}$, $\chi_{4,22}$), and comparing to a state-of-the-art IP-Glasma+MUSIC+UrQMD model, the authors extract experimental sensitivity to the diffuseness parameter $a_0$ and the quadrupole deformation $\beta_2$ of $^{129}$Xe. The data favor $\beta_2\approx0.207$ and $a_0\approx0.492$ for describing $v_2$-related observables, demonstrating the feasibility of constraining nuclear deformation and diffuseness at TeV energies; these results motivate a future Bayesian analysis to robustly extract the structure parameters and to extend such studies to other nuclei and configurations. Overall, the work establishes multiparticle flow observables as a powerful probe of nuclear structure in high-energy collisions and complements low-energy nuclear structure studies, with potential to explore alpha-clustering in light systems in upcoming runs.

Abstract

Details of the nuclear structure of $^{\rm 129}$Xe, such as the quadrupole deformation and the nuclear diffuseness, are studied by extensive measurements of anisotropic-flow-related observables in Xe--Xe collisions at a centre-of-mass energy per nucleon pair $\sqrt{s_{_{\mathrm{NN}}}}~=~5.44$ TeV with the ALICE detector at the LHC. The results are compared with those from Pb--Pb collisions at $\sqrt{s_{_{\mathrm{NN}}}}~=~5.02$ TeV for a baseline, given that the $^{\rm 208}$Pb nucleus exhibits a very weak deformation. Furthermore, comprehensive comparisons are performed with a state-of-the-art hybrid model using IP-Glasma+MUSIC+UrQMD. It is found that among various IP-Glasma+MUSIC+UrQMD calculations with different values of nuclear parameters, the one using a nuclear diffuseness parameter of $a_0=0.492$ and a nuclear quadrupole deformation parameter of $β_2=0.207$ provides a better description of the presented flow measurements. These studies represent the first systematic exploration of nuclear structure at TeV energies, utilizing a comprehensive set of anisotropic flow observables. The measurements serve as a critical experimental benchmark for rigorously testing the interplay between nuclear structure inputs and heavy-ion theoretical models.

Figures (7)

• Figure 1: Panels (a) and (b): Charged particle $v_2\{2, \hbox{$\left | \Delta\eta \right | > 1.0$}\}$ (left) and $v_2\{4\}$ (right) as a function of centrality in Xe--Xe and Pb--Pb collisions at $\sqrt{s_{_{\mathrm{NN}}}}~=~5.44$ TeemV and $\sqrt{s_{_{\mathrm{NN}}}}~=~5.02$ TeemV, respectively. Panels (c) and (d): Ratio between Xe--Xe and Pb--Pb $v_2\{2, \hbox{$\left | \Delta\eta \right | > 1.0$}\}$ (left) and $v_2\{4\}$ (right). Statistical and systematical uncertainties are shown as vertical lines and grey boxes, respectively. The measurements are compared with IP-Glasma+MUSIC+UrQMD calculations Schenke:2020mboMantysaari:2022ffw to constrain the $\beta_2$ and $a_0$ parameters of $^{129}$Xe nuclei. The thickness of the bands represent statistical uncertainties.
• Figure 2: Panels (a) and (b): Charged particle $\langle v_2 \rangle$ (left) and $\sigma_{v_2}$ (right) as a function of centrality in Xe--Xe and Pb--Pb collisions at $\sqrt{s_{_{\mathrm{NN}}}}~=~5.44$ TeemV and $\sqrt{s_{_{\mathrm{NN}}}}~=~5.02$ TeemV, respectively. Panels (c) and (d): Ratio between Xe--Xe and Pb--Pb $\langle v_2 \rangle$ (left) and $\sigma_{v_2}$ (right). Statistical and systematical uncertainties are shown as vertical lines and grey boxes, respectively. The measurements are compared with IP-Glasma+MUSIC+UrQMD calculations Schenke:2020mboMantysaari:2022ffw to constrain the $\beta_2$ and $a_0$ parameters of $^{129}$Xe nuclei. The thickness of the bands represent statistical uncertainties.
• Figure 3: Panels (a) and (b): Charged particle $v_3\{2, \hbox{$\left | \Delta\eta \right | > 0.8$}\}$ (left) and $v_4\{2, \hbox{$\left | \Delta\eta \right | > 0.8$}\}$ (right) as a function of centrality in Xe--Xe and Pb--Pb collisions at $\sqrt{s_{_{\mathrm{NN}}}}~=~5.44$ TeemV and $\sqrt{s_{_{\mathrm{NN}}}}~=~5.02$ TeemV, respectively. Panels (c) and (d): Ratio between Xe--Xe and Pb--Pb $v_3\{2, \hbox{$\left | \Delta\eta \right | > 0.8$}\}$ (left) and $v_4\{2, \hbox{$\left | \Delta\eta \right | > 0.8$}\}$ (right). Statistical and systematical uncertainties are shown as vertical lines and grey boxes, respectively. The measurements are compared with IP-Glasma+MUSIC+UrQMD calculations Schenke:2020mboMantysaari:2022ffw to constrain the $\beta_2$ and $a_0$ parameters of $^{129}$Xe nuclei. The thickness of the bands represent statistical uncertainties.
• Figure 4: Panels (a) and (b): Charged particle $v_{4,22}$ (left) and $\rho_{4,22}$ (right) as a function of centrality in Xe--Xe and Pb--Pb collisions at $\sqrt{s_{_{\mathrm{NN}}}}~=~5.44$ TeemV and $\sqrt{s_{_{\mathrm{NN}}}}~=~5.02$ TeemV, respectively. Panels (c) and (d): Ratio between Xe--Xe and Pb--Pb $v_{4,22}$ (left) and $\rho_{4,22}$ (right). Statistical and systematical uncertainties are shown as vertical lines and grey boxes, respectively. The measurements are compared with IP-Glasma+MUSIC+UrQMD calculations Schenke:2020mboMantysaari:2022ffw to constrain the $\beta_2$ and $a_0$ parameters of $^{129}$Xe nuclei. The thickness of the bands represent statistical uncertainties.
• Figure 5: Values of $\chi^2/N_{\rm dof}$ between the measurements (Xe--Xe/Pb--Pb) and the calculations (Xe--Xe/Pb--Pb). The x-axis represents the different measured observables, and the y-axis is shown on a logarithmic scale. Panels (a) and (b) show the results for the 0--20% and 20--60% centrality ranges, respectively.