Two-particle transverse momentum correlations in pp and p-Pb collisions at LHC energies

The collaboration
CERN-EP-2022-230, 2022.

Abstract (data abstract)
Two-particle transverse momentum differential correlators, recently measured in Pb$-$Pb collisions at LHC energies, provide an additional tool to gain insights into particle production mechanisms and infer transport properties, such as the ratio of shear viscosity to entropy density, of the medium created in Pb$-$Pb collisions. The longitudinal long-range correlations and the large azimuthal anisotropy measured at low transverse momenta in small collision systems, namely pp and p$-$Pb, at LHC energies resemble manifestations of collective behaviour. This suggests that locally equilibrated matter may be produced in these small collision systems, similar to what is observed in Pb$-$Pb collisions. In this work, the same two-particle transverse momentum differential correlators are exploited in pp and p$-$Pb collisions at $\sqrt{s} = 7\;\text{TeV}$ and $\sqrt{s_{\rm NN}} = 5.02\;\text{TeV}$, respectively, to seek evidence for viscous effects. Specifically, the strength and shape of the correlators are studied as a function of the produced particle multiplicity to identify evidence for longitudinal broadening that might reveal the presence of viscous effects in these smaller systems. The measured correlators and their evolution from pp and p$-$Pb to Pb$-$Pb collisions are additionally compared to predictions from Monte Carlo event generators, and the potential presence of viscous effects is discussed.

• #### Figure 1.1

Data from Figure 1 (top left).

10.17182/hepdata.137819.v1/t1

Two-particle transverse momentum correlation $G_{2}^{\rm CD}$ for 0$-$5% multiplicity class pp collisions at $\sqrt{s}=7\;\text{TeV}$.

• #### Figure 1.2

Data from Figure 1 (top central).

10.17182/hepdata.137819.v1/t2

Two-particle transverse momentum correlation $G_{2}^{\rm CD}$ for 30$-$40% multiplicity class pp collisions at $\sqrt{s}=7\;\text{TeV}$.

• #### Figure 1.3

Data from Figure 1 (top right).

10.17182/hepdata.137819.v1/t3

Two-particle transverse momentum correlation $G_{2}^{\rm CD}$ for 70$-$80% multiplicity class pp collisions at $\sqrt{s}=7\;\text{TeV}$.

• #### Figure 1.4

Data from Figure 1 (bottom left).

10.17182/hepdata.137819.v1/t4

Two-particle transverse momentum correlation $G_{2}^{\rm CI}$ for 0$-$5% multiplicity class pp collisions at $\sqrt{s}=7\;\text{TeV}$.

• #### Figure 1.5

Data from Figure 1 (bottom central).

10.17182/hepdata.137819.v1/t5

Two-particle transverse momentum correlation $G_{2}^{\rm CI}$ for 30$-$40% multiplicity class pp collisions at $\sqrt{s}=7\;\text{TeV}$.

• #### Figure 1.6

Data from Figure 1 (bottom right).

10.17182/hepdata.137819.v1/t6

Two-particle transverse momentum correlation $G_{2}^{\rm CI}$ for 70$-$80% multiplicity class pp collisions at $\sqrt{s}=7\;\text{TeV}$.

• #### Figure 2.1

Data from Figure 2 (top left).

10.17182/hepdata.137819.v1/t7

Two-particle transverse momentum correlation $G_{2}^{\rm CD}$ for 0$-$5% multiplicity class p$-$Pb collisions at $\sqrt{s_{\rm NN}}=5.02\;\text{TeV}$.

• #### Figure 2.2

Data from Figure 2 (top central).

10.17182/hepdata.137819.v1/t8

Two-particle transverse momentum correlation $G_{2}^{\rm CD}$ for 30$-$40% multiplicity class p$-$Pb collisions at $\sqrt{s_{\rm NN}}=5.02\;\text{TeV}$.

• #### Figure 2.3

Data from Figure 2 (top right).

10.17182/hepdata.137819.v1/t9

Two-particle transverse momentum correlation $G_{2}^{\rm CD}$ for 70$-$80% multiplicity class p$-$Pb collisions at $\sqrt{s_{\rm NN}}=5.02\;\text{TeV}$.

• #### Figure 2.4

Data from Figure 2 (bottom left).

10.17182/hepdata.137819.v1/t10

Two-particle transverse momentum correlation $G_{2}^{\rm CI}$ for 0$-$5% multiplicity class p$-$Pb collisions at $\sqrt{s_{\rm NN}}=5.02\;\text{TeV}$.

• #### Figure 2.5

Data from Figure 2 (bottom central).

10.17182/hepdata.137819.v1/t11

Two-particle transverse momentum correlation $G_{2}^{\rm CI}$ for 30$-$40% multiplicity class p$-$Pb collisions at $\sqrt{s_{\rm NN}}=5.02\;\text{TeV}$.

• #### Figure 2.6

Data from Figure 2 (bottom right).

10.17182/hepdata.137819.v1/t12

Two-particle transverse momentum correlation $G_{2}^{\rm CI}$ for 70$-$80% multiplicity class p$-$Pb collisions at $\sqrt{s_{\rm NN}}=5.02\;\text{TeV}$.

• #### Figure 3.1

Data from Figure 3 (top left).

10.17182/hepdata.137819.v1/t13

Near side ($|\Delta\varphi| < \pi/2$) longitudinal projection of the two-particle transverse momentum correlation $G_{2}^{\rm CD}$ for 0$-$5%, 30$-$40%, and 70$-$80%...

• #### Figure 3.2

Data from Figure 3 (top right).

10.17182/hepdata.137819.v1/t14

Azimuthal projection ($|\Delta\eta|<1.6$) of the two-particle transverse momentum correlation $G_{2}^{\rm CD}$ for 0$-$5%, 30$-$40%, and 70$-$80% multiplicity classes pp collisions...

• #### Figure 3.3

Data from Figure 3 (bottom left).

10.17182/hepdata.137819.v1/t15

Near side ($|\Delta\varphi| < \pi/2$) longitudinal projection of the two-particle transverse momentum correlation $G_{2}^{\rm CI}$ for 0$-$5%, 30$-$40%, and 70$-$80%...

• #### Figure 3.4

Data from Figure 3 (bottom right).

10.17182/hepdata.137819.v1/t16

Azimuthal projection ($|\Delta\eta|<1.6$) of the two-particle transverse momentum correlation $G_{2}^{\rm CI}$ for 0$-$5%, 30$-$40%, and 70$-$80% multiplicity classes pp collisions...

• #### Figure 4.1

Data from Figure 4 (top left).

10.17182/hepdata.137819.v1/t17

Near side ($|\Delta\varphi| < \pi/2$) longitudinal projection of the two-particle transverse momentum correlation $G_{2}^{\rm CD}$ for 0$-$5%, 30$-$40%, and 70$-$80%...

• #### Figure 4.2

Data from Figure 4 (top right).

10.17182/hepdata.137819.v1/t18

Azimuthal projection ($|\Delta\eta|<1.6$) of the two-particle transverse momentum correlation $G_{2}^{\rm CD}$ for 0$-$5%, 30$-$40%, and 70$-$80% multiplicity classes p$-$Pb collisions...

• #### Figure 4.3

Data from Figure 4 (bottom left).

10.17182/hepdata.137819.v1/t19

Near side ($|\Delta\varphi| < \pi/2$) longitudinal projection of the two-particle transverse momentum correlation $G_{2}^{\rm CI}$ for 0$-$5%, 30$-$40%, and 70$-$80%...

• #### Figure 4.4

Data from Figure 4 (bottom right).

10.17182/hepdata.137819.v1/t20

Azimuthal projection ($|\Delta\eta|<1.6$) of the two-particle transverse momentum correlation $G_{2}^{\rm CI}$ for 0$-$5%, 30$-$40%, and 70$-$80% multiplicity classes p$-$Pb collisions...

• #### Figure 5.1

Data from Figure 5 (top left).

10.17182/hepdata.137819.v1/t21

Evolution with the average charged particle multiplicity of the longitudinal widths of the two-particle transverse momentum differential correlation $G_{2}^{\rm CD}$...

• #### Figure 5.2

Data from Figure 5 (top right).

10.17182/hepdata.137819.v1/t22

Evolution with the average charged particle multiplicity of the azimuthal widths of the two-particle transverse momentum differential correlation $G_{2}^{\rm CD}$...

• #### Figure 5.3

Data from Figure 5 (bottom left).

10.17182/hepdata.137819.v1/t23

Evolution with the average charged particle multiplicity of the longitudinal widths of the two-particle transverse momentum differential correlation $G_{2}^{\rm CI}$...

• #### Figure 5.4

Data from Figure 5 (bottom right).

10.17182/hepdata.137819.v1/t24

Evolution with the average charged particle multiplicity of the azimuthal widths of the two-particle transverse momentum differential correlation $G_{2}^{\rm CI}$...

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