Understanding nuclear structure provides essential insights into the properties of atomic nuclei. In this paper, 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 center-of-mass energy per nucleon pair $\sqrt{s_{\rm NN}} = 5.44$ TeV with the ALICE detector at the LHC. The results are compared with those from Pb$-$Pb collisions at $\sqrt{s_{\rm NN}} = 5.02$ TeV for a baseline, given that the $^{\rm 208}$Pb nucleus is not deformed. 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 $\beta_2=0.207$ provides a better description of the presented flow measurements. These studies represent an important step towards a thorough exploration of the imaging power of nuclear collisions at ultrarelativistic energy and the search for the imprint of nuclear structure on various flow observables in heavy-ion collisions at the LHC. The findings demonstrate the potential of nuclear structure studies at the TeV energy scale and highlight that the LHC experiments can complement existing low-energy experiments on nuclear structure studies.
Submitted to: PLB
e-Print: arXiv:2409.04343 | PDF | inSPIRE
CERN-EP-2024-228
Figure group
Figure 1
Panels (a) and (b): Charged particle $v_2\{2, \left | \Delta\eta \right | > 1.0\}$ (left) and $v_2\{4\}$ (right) as a function of centrality in Xe--Xe and Pb--Pb collisions at $\sqrt{s_{_{\mathrm{NN}}}} = 5.44$ TeV and $\sqrt{s_{_{\mathrm{NN}}}} = 5.02$ TeV, respectively. Panels (c) and (d): Ratio between Xe--Xe and Pb--Pb $v_2\{2, \left | \Delta\eta \right | > 1.0\}$ (left) and $v_2\{4\}$ (right). Statistical and systematical uncertainties are shown as vertical lines and gray boxes, respectively. The measurements are compared with IP-Glasma+MUSIC+UrQMD calculations to constrain the $\beta_2$ and $a_0$ parameters of $^{129}$Xe nuclei. |  |
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 $\sqrt{s_{_{\mathrm{NN}}}} = 5.44$ TeV and $\sqrt{s_{_{\mathrm{NN}}}} = 5.02$ TeV, 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 gray boxes, respectively. The measurements are compared with IP-Glasma+MUSIC+UrQMD calculations to constrain the $\beta_2$ and $a_0$ parameters of $^{129}$Xe nuclei. |  |
Figure 3
Panels (a) and (b): Charged particle $v_3\{2, \left | \Delta\eta \right | > 0.8\}$ (left) and $v_4\{2, \left | \Delta\eta \right | > 0.8\}$ (right) as a function of centrality in Xe--Xe and Pb--Pb collisions at $\sqrt{s_{_{\mathrm{NN}}}} = 5.44$ TeV and $\sqrt{s_{_{\mathrm{NN}}}} = 5.02$ TeV, respectively. Panels (c) and (d): Ratio between Xe--Xe and Pb--Pb $v_3\{2, \left | \Delta\eta \right | > 0.8\}$ (left) and $v_4\{2, \left | \Delta\eta \right | > 0.8\}$ (right). Statistical and systematical uncertainties are shown as vertical lines and gray boxes, respectively. The measurements are compared with IP-Glasma+MUSIC+UrQMD calculations to constrain the $\beta_2$ and $a_0$ parameters of $^{129}$Xe nuclei. |  |
Figure 4
Panels (a) and (b): Charged particle $v_4^{\rm L}$ (left) and $v_{4,22}$ (right) as a function of centrality in Xe--Xe and Pb--Pb collisions at $\sqrt{s_{_{\mathrm{NN}}}} = 5.44$ TeV and $\sqrt{s_{_{\mathrm{NN}}}} = 5.02$ TeV, respectively. Panels (c) and (d): Ratio between Xe--Xe and Pb--Pb $v_4^{\rm L}$ (left) and $v_{4,22}$ (right). Statistical and systematical uncertainties are shown as vertical lines and gray boxes, respectively. The measurements are compared with IP-Glasma+MUSIC+UrQMD calculations to constrain the $\beta_2$ and $a_0$ parameters of $^{129}$Xe nuclei. |  |
Figure 5
Panels (a) and (b): Charged particle $\chi_{4,22}$ (left) and $\rho_{4,22}$ (right) as a function of centrality in Xe--Xe and Pb--Pb collisions at $\sqrt{s_{_{\mathrm{NN}}}} = 5.44$ TeV and $\sqrt{s_{_{\mathrm{NN}}}} = 5.02$ TeV, respectively. Panels (c) and (d): Ratio between Xe--Xe and Pb--Pb $\chi_{4,22}$ (left) and $\rho_{4,22}$ (right). Statistical and systematical uncertainties are shown as vertical lines and gray boxes, respectively. The measurements are compared with IP-Glasma+MUSIC+UrQMD calculations to constrain the $\beta_2$ and $a_0$ parameters of $^{129}$Xe nuclei. |  |
Figure 6
Top Panel: Charged particle NSC$(3,2)$ as a function of centrality in Xe--Xe and Pb--Pb collisions at $\sqrt{s_{_{\mathrm{NN}}}} = 5.44$ TeV and $\sqrt{s_{_{\mathrm{NN}}}} = 5.02$ TeV, respectively. Bottom Panel: Ratio between Xe--Xe and Pb--Pb NSC$(3,2)$. Statistical and systematical uncertainties are shown as vertical lines and gray boxes, respectively. The measurements are compared with IP-Glasma+MUSIC+UrQMD calculations to constrain the $\beta_2$ and $a_0$ parameters of $^{129}$Xe nuclei. |  |
