Anisotropic flow and flow fluctuations of identified hadrons in Pb$-$Pb collisions at $\sqrt{s_{\mathrm{NN}}}$ = 5.02 TeV

The first measurements of elliptic flow of $\pi^\pm$, ${\rm K}^\pm$, p+$\overline{\rm p}$, ${\rm K_{S}^0}$, $\Lambda$+$\overline{\Lambda}$, $\phi$, $\Xi^-$+$\Xi^+$, and $\Omega^-$+$\Omega^+$ using multiparticle cumulants in Pb$-$Pb collisions at $\sqrt{s_{\rm NN}}$ = 5.02 TeV are presented. Results obtained with two- ($v_2\{2\}$) and four-particle cumulants ($v_2\{4\}$) are shown as a function of transverse momentum, $p_{\rm T}$, for various collision centrality intervals. Combining the data for both $v_2\{2\}$ and $v_2\{4\}$ also allows us to report the first measurements of the mean elliptic flow, elliptic flow fluctuations, and relative elliptic flow fluctuations for various hadron species. These observables probe the event-by-event eccentricity fluctuations in the initial state and the contributions from the dynamic evolution of the expanding quark-gluon plasma. The characteristic features observed in previous $p_{\rm T}$-differential anisotropic flow measurements for identified hadrons with two-particle correlations, namely the mass ordering at low $p_{\rm T}$ and the approximate scaling with the number of constituent quarks at intermediate $p_{\rm T}$, are similarly present in the four-particle correlations and the combinations of $v_2\{2\}$ and $v_2\{4\}$. In addition, a particle species dependence of flow fluctuations is observed that could indicate a significant contribution from final state hadronic interactions. The comparison between experimental measurements and CoLBT model calculations, which combine the various physics processes of hydrodynamics, quark coalescence, and jet fragmentation, illustrates their importance over a wide $p_{\rm T}$ range.

 

Submitted to: JHEP
e-Print: arXiv:2206.04587 | PDF | inSPIRE
CERN-EP-2022-122
Figure group

Figure 1

Simultaneous fits on invariant mass distribution, 〈〈2′〉〉, and 〈〈4′〉〉 correlations of K0 S meson at 1.1< pT < 1.3 GeV/c for centrality 40–50% in √sNN = 5.02 TeV Pb–Pb collisions.

Figure 2

The \pt-differential $v_2$ measured with two-particle correlations with a pseudorapidity gap of $|\Delta \eta| > 0.8$ for different particle species and centralities in Pb--Pb collisions at $\sqrt{s_{\mathrm{NN}}} = 5.02$~TeV..

Figure 3

The \pT-differential $v_2$ measured with four-particle cumulants ($v_2\{4\}$) for different particle species and centralities in Pb--Pb collisions at $\sqrt{s_{\mathrm{NN}}} = 5.02$~TeV..

Figure 4

The dependence of $v_2\{4\}/n_{\rm q}$ on $\pt/n_{\rm q}$, where $n_{\rm q}$ is the number of constituents quarks, for different particle species and centralities in Pb--Pb collisions at $\sqrt{s_{\mathrm{NN}}} = 5.02$~TeV..

Figure 5

The dependence of the mean value of $v_2$ ($\langle v_2 \rangle$) on \pt{} for different particle species and centralities in Pb--Pb collisions at $\sqrt{s_{\mathrm{NN}}} = 5.02$~TeV..

Figure 6

The \pt{} dependence of the standard deviation of $v_2$ ($\sigma_{\rm v_2}$) for different particle species and centralities in Pb--Pb collisions at $\sqrt{s_{\mathrm{NN}}} = 5.02$~TeV..

Figure 7

The relative elliptic flow fluctuations ($F(v_2)$) as a function of \pt{} for different particle species and centralities in Pb--Pb collisions at $\sqrt{s_{\mathrm{NN}}} = 5.02$~TeV..

Figure 8

The ratio $v_2\{4\}/v_2\{2,|\Delta \eta| > 0.8\}$ as a function of \pt{} for different particle species and centralities in Pb--Pb collisions at $\sqrt{s_{\mathrm{NN}}} = 5.02$~TeV. .

Figure 9

The \pt-differential $v_2\{4\}$ for \pipm{}, \kapm{}, and p+\pbar{} measured in Pb--Pb collisions at $\sqrt{s_{\mathrm{NN}}} = 5.02$~TeV compared with expectations of the same quantity from the CoLBT hydrodynamic model with quark coalescence~. The left and right panels present the comparison for the 10--20\% and 40--50\% centrality intervals, respectively. The thickness of the curves reflect the uncertainties of the hydrodynamic calculations..

Figure 10

The \pt-differential $v_2\{4\}$ for \pipm{}, \kapm{}, and p+\pbar{} measured in Pb--Pb collisions at $\sqrt{s_{\mathrm{NN}}} = 5.02$~TeV compared with expectations of the same quantity from the CoLBT hydrodynamic model without quark coalescence~ in 40--50\% centrality interval. The thickness of the curves reflect the uncertainties of the hydrodynamic calculations..

Figure 11

The \pt-differential (a) $\langle v_2 \rangle$, (b) $\sigma_{v_2}$, (c) $v_2\{4\}/v_2\{2\}$, and (d) $F(v_2)$ for \pipm{}, \kapm{}, and p+\pbar{} measured in one indicative centrality interval (40--50\%) of Pb--Pb collisions at $\sqrt{s_{\mathrm{NN}}} = 5.02$~TeV compared with expectations of the same quantities from the CoLBT hydrodynamic model~. The thickness of the curves reflect the uncertainties of the hydrodynamic calculations..

Figure 12

The \pt-differential (a) $\langle v_2 \rangle$, (b) $\sigma_{v_2}$, (c) $v_2\{4\}/v_2\{2\}$, and (d) $F(v_2)$ for \pipm{}, \kapm{}, and p+\pbar{} measured in one indicative centrality interval (40--50\%) of Pb--Pb collisions at $\sqrt{s_{\mathrm{NN}}} = 5.02$~TeV compared with expectations of the same quantities from the CoLBT hydrodynamic model without quark coalescence~. The thickness of the curves reflect the uncertainties of the hydrodynamic calculations..