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Direct photon elliptic flow in Pb-Pb collisions at $\sqrt{s_{\rm NN}}$ = 2.76 TeV

The collaboration
Phys.Lett. B789 (2019) 308-322, 2019

Abstract (data abstract)
The elliptic flow of inclusive and direct photons was measured at mid-rapidity in two centrality classes 0--20\% and 20--40\% in Pb--Pb collisions at $\sqrt{s_{\rm NN}} = 2.76$ TeV by ALICE. Photons were detected with the highly segmented electromagnetic calorimeter PHOS and via conversions in the detector material with the $e^+e^-$ pairs reconstructed in the central tracking system. The results of the two methods were combined and the direct photon elliptic flow was extracted in the transverse momentum range $0.9 < p_\text{T} < 6.2$ GeV/$c$. We test the hypothesis $v_{2}^{\gamma,dir} \equiv 0$ for $0.9 < p_\text{T} < 2.1$ GeV/$c$ and obtain a significance of $1.4\sigma$ for the 0--20\% class and $1.0\sigma$ for the 20--40\% class. A comparison to RHIC data shows a similar magnitude of the measured elliptic flow, while hydrodynamic and transport model calculations predict a smaller flow than observed.

• #### Table 1

Figure 1

10.17182/hepdata.88050.v1/t1

Ratio V2{GAMMA,INCLUSIVE,PCM}/V2{GAMMA,INCLUSIVE,COMBINED} as function of $p_\text{T}$, collision centrality 0-20%, for Pb-Pb collisions at $\sqrt{s_{\rm NN}} = 2.76$ TeV.

• #### Table 2

Figure 1

10.17182/hepdata.88050.v1/t2

Ratio V2{GAMMA,INCLUSIVE,PHOS}/V2{GAMMA,INCLUSIVE,COMBINED} as function of $p_\text{T}$, collision centrality 20-40%, for Pb-Pb collisions at $\sqrt{s_{\rm NN}} = 2.76$ TeV.

• #### Table 3

Figure 2

10.17182/hepdata.88050.v1/t3

V2{GAMMA,DECAY} as function of $p_\text{T}$, collision centrality 0-20%, for Pb-Pb collisions at $\sqrt{s_{\rm NN}} = 2.76$ TeV.

• #### Table 4

Figure 2

10.17182/hepdata.88050.v1/t4

V2{GAMMA,DECAY} as function of $p_\text{T}$, collision centrality 20-40%, for Pb-Pb collisions at $\sqrt{s_{\rm NN}} = 2.76$ TeV.

• #### Table 5

Figure 3

10.17182/hepdata.88050.v1/t5

V2{GAMMA,INCLUSIVE} as function of $p_\text{T}$, collision centrality 0-20%, for Pb-Pb collisions at $\sqrt{s_{\rm NN}} = 2.76$ TeV.

• #### Table 6

Figure 3

10.17182/hepdata.88050.v1/t6

V2{GAMMA,INCLUSIVE} as function of $p_\text{T}$, collision centrality 20-40%, for Pb-Pb collisions at $\sqrt{s_{\rm NN}} = 2.76$ TeV.

• #### Table 7

Figure 5

10.17182/hepdata.88050.v1/t7

V2{GAMMA,DIRECT} as function of $p_\text{T}$, collision centrality 0-20%, for Pb-Pb collisions at $\sqrt{s_{\rm NN}} = 2.76$ TeV.

• #### Table 8

Figure 5

10.17182/hepdata.88050.v1/t8

V2{GAMMA,DIRECT} as function of $p_\text{T}$, collision centrality 20-40%, for Pb-Pb collisions at $\sqrt{s_{\rm NN}} = 2.76$ TeV.