General balance functions of identified charged hadron pairs of $(\pi,{\rm K},{\rm p})$ in Pb$-$Pb collisions at $\sqrt{s_{\rm NN}} = 2.76$ TeV

The collaboration
Phys.Lett.B 833 (2022) 137338, 2022.

Abstract (data abstract)
First measurements of balance functions (BF) of all combinations of identified charged hadron $(\pi,\rm K,\rm p)$ pairs in Pb--Pb collisions at $\sqrt{s_{_{\rm NN}}} =$2.76 TeV recorded by the ALICE detector are presented. The BF measurements are carried out as two-dimensional differential correlators versus the relative rapidity ($\Delta y$) and azimuthal angle ($\Delta\varphi$) of hadron pairs, and studied as a function of collision centrality. The $\Delta\varphi$ dependence of BF is expected to be sensitive to the light quark diffusivity in the quark--gluon plasma. While the BF azimuthal widths of all pairs substantially decrease from peripheral to central collisions, the longitudinal widths exhibit mixed behaviors: BF of $\pi\pi$ and cross-species pairs narrow in more central collisions, whereas those of $\rm KK$ and $\rm pp$ are found to be independent of collision centrality. This dichotomy is qualitatively consistent with the presence of strong radial flow effects and the existence of two-stage quark production in relativistic heavy-ion collisions. Finally, the first measurements of the collision centrality evolution of BF integrals are presented, with the observation that relative charge balancing fractions are nearly independent of collision centrality in Pb--Pb collisions. Overall, the results presented provide new and challenging constraints for theoretical models of hadron production and transport in relativistic heavy-ion collisions.

• Figure 1.1

Data from Figure 1 (left).

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Balance function $B^{\pi\pi}$ measured in semicentral Pb--Pb collisions at $\sqrt{s_{\rm NN}}=2.76\;\text{TeV}$ ($\pi,{\rm K}: 0.2 \leq p_{\rm T} \leq 2.0\;{\rm GeV}/c$;...

• Figure 1.2

Data from Figure 1 (central).

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• Figure 2.1

Data from Figure 2 (top left).

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Balance function $B^{\pi\pi}$ projected onto the $\Delta y$ axis for particle pairs within the full range $|\Delta\varphi|\leq \pi$ in Pb--Pb...

• Figure 2.2

Data from Figure 2 (middle left).

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Balance function $B^{{\rm K}\pi}$ projected onto the $\Delta y$ axis for particle pairs within the full range $|\Delta\varphi|\leq \pi$ in...

• Figure 2.3

Data from Figure 2 (bottom left).

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Balance function $B^{{\rm p}\pi}$ projected onto the $\Delta y$ axis for particle pairs within the full range $|\Delta\varphi|\leq \pi$ in...

• Figure 2.4

Data from Figure 2 (top center).

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Balance function $B^{\pi{\rm K}}$ projected onto the $\Delta y$ axis for particle pairs within the full range $|\Delta\varphi|\leq \pi$ in...

• Figure 2.5

Data from Figure 2 (middle center).

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Balance function $B^{{\rm KK}}$ projected onto the $\Delta y$ axis for particle pairs within the full range $|\Delta\varphi|\leq \pi$ in...

• Figure 2.6

Data from Figure 2 (bottom center).

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Balance function $B^{{\rm pK}}$ projected onto the $\Delta y$ axis for particle pairs within the full range $|\Delta\varphi|\leq \pi$ in...

• Figure 2.7

Data from Figure 2 (top right).

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Balance function $B^{\pi{\rm p}}$ projected onto the $\Delta y$ axis for particle pairs within the full range $|\Delta\varphi|\leq \pi$ in...

• Figure 2.8

Data from Figure 2 (middle right).

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Balance function $B^{{\rm Kp}}$ projected onto the $\Delta y$ axis for particle pairs within the full range $|\Delta\varphi|\leq \pi$ in...

• Figure 2.9

Data from Figure 2 (bottom right).

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Balance function $B^{{\rm pp}}$ projected onto the $\Delta y$ axis for particle pairs within the full range $|\Delta\varphi|\leq \pi$ in...

• Figure 3.1

Data from Figure 3 (top left).

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