Correlations among conserved quantum numbers, such as the net-electric charge, the net-baryon, and the net-strangeness in heavy-ion collisions, are crucial for exploring the QCD phase diagram. In this letter, these correlations are investigated using net-proton number (as a proxy for the net-baryon), net-kaon number (for the net-strangeness), and net-charged particle number in Pb-Pb collisions at $\sqrt{s_\text{NN}}=5.02$ TeV with the ALICE detector. The observed correlations deviate from the Poissonian baseline, with a more pronounced deviation at LHC energies than at RHIC. Theoretical calculations of the Thermal-FIST hadron resonance gas model, HIJING, and EPOS LHC event generators are compared with experimental results, where a significant impact of resonance decays is observed. Thermal-FIST calculations under the grand canonical and canonical ensembles highlight significant differences, underscoring the role of local charge conservation in explaining the data. Recent lattice QCD studies have demonstrated that the magnetic field generated by spectator protons in heavy-ion collisions affects susceptibility ratios, in particular those related to the net-electric charge and the net-baryon numbers. The experimental findings are in qualitative agreement with the expectations of lattice QCD.
Submitted to: JHEP
e-Print: arXiv:2503.18743 | PDF | inSPIRE
Figure group
Figure 1
Centrality dependence of diagonal cumulants ($\kappa^{2}_{\alpha}$) and off-diagonal cumulants ($\kappa^{11}_{\alpha,\beta}$) for the net-pion, net-kaon, net-proton, and net-charged particle distributions in Pb--Pb collisions at $\sqrt{s_\mathrm{NN}}=5.02$ TeV. The measurements are shown for two different $p_\mathrm{T}$ ranges. The statistical (systematic) uncertainties are represented by vertical bars (boxes). |  |
Figure 2
Centrality dependence of correlations $C_\mathrm{Q,p}$ (top), $C_\mathrm{Q,K}$ (middle), and $C_\mathrm{p,K}$ (bottom) in Pb--Pb collisions at $\sqrt{s_\mathrm{NN}}=5.02$ TeV. The measurements are shown for two different $p_\mathrm{T}$ ranges in left and right columns. The predictions from HIJING , EPOS LHC , and Thermal-FIST (TheFIST) model calculations with the grand canonical ensemble (GCE) and canonical ensemble (CE) formulation are denoted by colored lines. In the CE calculations, the electric charge (Q), baryon number (B), and strangeness (S) are conserved in a correlation volume of $V_c=3\mathrm{d}V/\mathrm{d}y$. The statistical (systematic) uncertainties are represented by vertical bars (boxes), and the dashed line corresponds to the Poisson baseline. |  |
Figure 3
Correlations $C_\mathrm{p,K}$ (left), $C_\mathrm{Q,p}$ (middle), and $C_\mathrm{Q,K}$ (right) are shown as a function of centrality in Pb--Pb collisions at $\sqrt{s_\mathrm{NN}}=5.02$ TeV. Colored lines represent Thermal-FIST (TheFIST) model calculations for the canonical ensemble (CE) with different correlation volumes ($V_{c}$). The statistical (systematic) uncertainties are represented by vertical bars (boxes). |  |
Figure 4
Correlations $C_\mathrm{p,K}$ (left), $C_\mathrm{Q,p}$ (middle), and $C_\mathrm{Q,K}$ (right) are shown as a function of centrality in Pb--Pb collisions at $\sqrt{s_\mathrm{NN}}=5.02$ TeV. Colored lines represent Thermal-FIST (TheFIST) model calculations for canonical ensemble (CE) with (w) and without (w/o) resonance contribution. The statistical (systematic) uncertainties are represented by vertical bars (boxes). |  |
Figure 5
Centrality dependence of $\kappa^{11}_\mathrm{Q,p}/\kappa^{2}_\mathrm{Q}$ (left) and $\kappa^{11}_\mathrm{Q,K}/\kappa^{2}_\mathrm{Q}$ (right) in Pb--Pb collisions at $\sqrt{s_\mathrm{NN}}=5.02$ TeV. Colored lines represent Thermal-FIST (TheFIST) model calculations for canonical ensemble (CE) with different correlation volumes ($V_{c}$). The statistical (systematic) uncertainties are represented by vertical bars (boxes). |  |
Figure 6
Centrality dependence of $(2\kappa^{11}_\mathrm{Q,K}-\kappa^{11}_\mathrm{p,K})/\kappa^{2}_\mathrm{K}$ (left) and $(2\kappa^{11}_\mathrm{Q,p}-\kappa^{11}_\mathrm{p,K})/\kappa^{2}_\mathrm{K}$ (right) in Pb--Pb collisions at $\sqrt{s_\mathrm{NN}}=5.02$ TeV. Thermal-FIST (TheFIST) model calculation for canonical ensemble (CE) with a correlation volume of $V_\mathrm{c}=2.6\mathrm{d}V/\mathrm{d}y$ is represented by the colored band. The statistical (systematic) uncertainties are represented by vertical bars (boxes). |  |
Figure 7
Centrality dependence of $(\kappa^{11}_\mathrm{Q,p}/\kappa^{2}_\mathrm{Q})/(\kappa^{11}_\mathrm{Q,p}/\kappa^{2}_\mathrm{Q})^{0-5\%}$ in Pb--Pb collisions at $\sqrt{s_\mathrm{NN}}=5.02$ TeV for Set 1 (left) and Set 2 (right) $p_\mathrm{T}$ acceptances. The colored bands represent the Thermal-FIST (TheFIST) model calculations for canonical ensemble (CE) with different $V_{c}$ values. The statistical (systematic) uncertainties are represented by vertical bars (boxes). |  |
Figure 8
Energy dependence of $C_\mathrm{p,K}$ (left), $C_\mathrm{Q,p}$ (middle), and $C_\mathrm{Q,K}$ (right), with lower energy results corresponding to STAR experiment . The statistical (systematic) uncertainties are represented by vertical bars (boxes) and the dashed line corresponds to Poisson baseline. |  |