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Longitudinal and azimuthal evolution of two-particle transverse momentum correlations in Pb-Pb collisions at $\sqrt{s_{\rm{NN}}}$ = 2.76 TeV

The collaboration
Phys.Lett. B804 (2020) 135375, 2020.

Abstract (data abstract)
This paper presents the first measurements of the charge independent (CI) and charge dependent (CD) two-particle transverse momentum correlators $G_{2}^{\rm CI}$ and $G_{2}^{\rm CD}$ in Pb--Pb collisions at $\sqrt{s_{\text{NN}}} = 2.76\;\text{TeV}$ by the ALICE collaboration. The correlators are measured as a function of pair separation in pseudorapidity ($\Delta \eta$) and azimuth ($\Delta \varphi$) and as a function of collision centrality.The correlator $G_{2}^{\rm CI}$ exhibits a longitudinal broadening while undergoing a monotonic azimuthal narrowing from peripheral to central collisions. By contrast, $G_{2}^{\rm CD}$ exhibits a narrowing along both dimensions towards central events. These features are not reproduced by models such as HIJING and AMPT. However, the observed narrowing of the correlators is expected to result from the stronger transverse flow profiles produced in more central collisions and the longitudinal broadening is predicted to be sensitive to momentum currents and the shear viscosity per unit of entropy density $\eta/s$ of the matter produced in the collisions. The observed broadening is found to be consistent with the hypothesized lower bound of $\eta/s$ and is in qualitative agreement with values obtained from anisotropic flow measurements.

• #### Figure 1.1

Data from Figure 1 (top left).

10.17182/hepdata.93887.v1/t1

Two-particle transverse momentum correlation $G_{2}^{\rm CI}$ for central (0-5%) Pb--Pb collisions at $\sqrt{s_{\rm NN}}=2.76\;\text{TeV}$.

• #### Figure 1.2

Data from Figure 1 (top central).

10.17182/hepdata.93887.v1/t2

Two-particle transverse momentum correlation $G_{2}^{\rm CI}$ for semi-central (30-40%) Pb--Pb collisions at $\sqrt{s_{\rm NN}}=2.76\;\text{TeV}$.

• #### Figure 1.3

Data from Figure 1 (top right).

10.17182/hepdata.93887.v1/t3

Two-particle transverse momentum correlation $G_{2}^{\rm CI}$ for perippheral (70-80%) Pb--Pb collisions at $\sqrt{s_{\rm NN}}=2.76\;\text{TeV}$.

• #### Figure 1.4

Data from Figure 1 (middle left).

10.17182/hepdata.93887.v1/t4

Near side ($|\Delta\varphi| < \pi/2$) longitudinal projection of the two-particle transverse momentum correlation $G_{2}^{\rm CI}$ for central (0-5%) Pb--Pb collisions...

• #### Figure 1.5

Data from Figure 1 (middle central).

10.17182/hepdata.93887.v1/t5

Near side ($|\Delta\varphi| < \pi/2$) longitudinal projection of the two-particle transverse momentum correlation $G_{2}^{\rm CI}$ for semi-central (30-40%) Pb--Pb collisions...

• #### Figure 1.6

Data from Figure 1 (middle right).

10.17182/hepdata.93887.v1/t6

Near side ($|\Delta\varphi| < \pi/2$) longitudinal projection of the two-particle transverse momentum correlation $G_{2}^{\rm CI}$ for perippheral (70-80%) Pb--Pb collisions...

• #### Figure 1.7

Data from Figure 1 (bottom left).

10.17182/hepdata.93887.v1/t7

Azimuthal projection ($|\Delta\eta|<1.6$) of the two-particle transverse momentum correlation $G_{2}^{\rm CI}$ for central (0-5%) Pb--Pb collisions at $\sqrt{s_{\rm NN}}=2.76\;\text{TeV}$. Systematic...

• #### Figure 1.8

Data from Figure 1 (bottom central).

10.17182/hepdata.93887.v1/t8

Azimuthal projection ($|\Delta\eta|<1.6$) of the two-particle transverse momentum correlation $G_{2}^{\rm CI}$ for semi-central (30-40%) Pb--Pb collisions at $\sqrt{s_{\rm NN}}=2.76\;\text{TeV}$. Systematic...

• #### Figure 1.9

Data from Figure 1 (bottom right).

10.17182/hepdata.93887.v1/t9

Azimuthal projection ($|\Delta\eta|<1.6$) of the two-particle transverse momentum correlation $G_{2}^{\rm CI}$ for perippheral (70-80%) Pb--Pb collisions at $\sqrt{s_{\rm NN}}=2.76\;\text{TeV}$. Systematic...

• #### Figure 2.1

Data from Figure 2 (top left).

10.17182/hepdata.93887.v1/t10

Collision centrality evolution of the longitudinal widths of the two-particle transverse momentum correlations $G_{2}^{\rm CI}$ and $G_{2}^{\rm CD}$ in Pb--Pb...

• #### Figure 2.2

Data from Figure 2 (top right).

10.17182/hepdata.93887.v1/t11

Collision centrality evolution of the azimuthal widths of the two-particle transverse momentum correlations $G_{2}^{\rm CI}$ and $G_{2}^{\rm CD}$ in Pb--Pb...

• #### Figure 4

Data from Figure 4.

10.17182/hepdata.93887.v1/t12

Longitudinal width evolution with the number of participants of the two-particle transverse momentum correlation $G_{2}^{\rm CI}$ in Pb--Pb collisions at...