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Azimuthally-differential pion femtoscopy relative to the third harmonic event plane in Pb-Pb collisions at $\mathbf{\sqrt{\textit{s}_{_{\rm NN}}}}$ = 2.76 TeV

The collaboration
Phys.Lett.B 785 (2018) 320-331, 2018.

Abstract
Azimuthally-differential femtoscopic measurements, being sensitive to spatio-temporal characteristics of the source as well as to the collective velocity fields at freeze out, provide very important information on the nature and dynamics of the system evolution. While the HBT radii oscillations relative to the second harmonic event plane measured recently reflect mostly the spatial geometry of the source, model studies have shown that the HBT radii oscillations relative to the third harmonic event plane are predominantly defined by the velocity fields. In this Letter, we present the first results on azimuthally-differential pion femtoscopy relative to the third harmonic event plane as a function of the pion pair transverse momentum $k_{\rm T}$ for different collision centralities in Pb-Pb collisions at $\sqrt{s_{\rm NN}}=2.76$ TeV. We find that the $R_{\rm side}$ and $R_{\rm out}$ radii, which characterize the pion source size in the directions perpendicular and parallel to the pion transverse momentum, oscillate in phase relative to the third harmonic event plane, similar to the results from 3+1D hydrodynamical calculations. The observed radii oscillations unambiguously signal a collective expansion and anisotropy in the velocity fields. A comparison of the measured radii oscillations with the Blast-Wave model calculations indicate that the initial state triangularity is washed-out at freeze out.

• #### Table 1

Data from Figure 1a

10.17182/hepdata.91129.v1/t1

The azimuthal dependence $R_{out}^2$ as function of $\Phi_{pair} - \Psi_{\mathrm{EP,3}}$ for the centrality 20-30% and different kT.

• #### Table 2

Data from Figure 1a

10.17182/hepdata.91129.v1/t2

The azimuthal dependence $R_{out}^2$ as function of $\Phi_{pair} - \Psi_{\mathrm{EP,3}}$ for the centrality 20-30% and different kT.

• #### Table 3

Data from Figure 1a

10.17182/hepdata.91129.v1/t3

The azimuthal dependence $R_{out}^2$ as function of $\Phi_{pair} - \Psi_{\mathrm{EP,3}}$ for the centrality 20-30% and different kT.

• #### Table 4

Data from Figure 1a

10.17182/hepdata.91129.v1/t4

The azimuthal dependence $R_{out}^2$ as function of $\Phi_{pair} - \Psi_{\mathrm{EP,3}}$ for the centrality 20-30% and different kT.

• #### Table 5

Data from Figure 1b

10.17182/hepdata.91129.v1/t5

The azimuthal dependence $R_{side}^2$ as function of $\Phi_{pair} - \Psi_{\mathrm{EP,3}}$ for the centrality 20-30% and different kT.

• #### Table 6

Data from Figure 1b

10.17182/hepdata.91129.v1/t6

The azimuthal dependence $R_{side}^2$ as function of $\Phi_{pair} - \Psi_{\mathrm{EP,3}}$ for the centrality 20-30% and different kT.

• #### Table 7

Data from Figure 1b

10.17182/hepdata.91129.v1/t7

The azimuthal dependence $R_{side}^2$ as function of $\Phi_{pair} - \Psi_{\mathrm{EP,3}}$ for the centrality 20-30% and different kT.

• #### Table 8

Data from Figure 1b

10.17182/hepdata.91129.v1/t8

The azimuthal dependence $R_{side}^2$ as function of $\Phi_{pair} - \Psi_{\mathrm{EP,3}}$ for the centrality 20-30% and different kT.

• #### Table 9

Data from Figure 1c

10.17182/hepdata.91129.v1/t9

The azimuthal dependence $R_{long}^2$ as function of $\Phi_{pair} - \Psi_{\mathrm{EP,3}}$ for the centrality 20-30% and different kT.

• #### Table 10

Data from Figure 1c

10.17182/hepdata.91129.v1/t10

The azimuthal dependence $R_{long}^2$ as function of $\Phi_{pair} - \Psi_{\mathrm{EP,3}}$ for the centrality 20-30% and different kT.

• #### Table 11

Data from Figure 1c

10.17182/hepdata.91129.v1/t11

The azimuthal dependence $R_{long}^2$ as function of $\Phi_{pair} - \Psi_{\mathrm{EP,3}}$ for the centrality 20-30% and different kT.

• #### Table 12

Data from Figure 1c

10.17182/hepdata.91129.v1/t12

The azimuthal dependence $R_{long}^2$ as function of $\Phi_{pair} - \Psi_{\mathrm{EP,3}}$ for the centrality 20-30% and different kT.

• #### Table 13

Data from Figure 2a

10.17182/hepdata.91129.v1/t13

Amplitudes of the radii oscillations as function of centrality percentile for four different $k_{\mathrm{T}}$.

• #### Table 14

Data from Figure 2a

10.17182/hepdata.91129.v1/t14

Amplitudes of the radii oscillations as function of centrality percentile for four different $k_{\mathrm{T}}$.

• #### Table 15

Data from Figure 2a

10.17182/hepdata.91129.v1/t15

Amplitudes of the radii oscillations as function of centrality percentile for four different $k_{\mathrm{T}}$.

• #### Table 16

Data from Figure 2a

10.17182/hepdata.91129.v1/t16

Amplitudes of the radii oscillations as function of centrality percentile for four different $k_{\mathrm{T}}$.

• #### Table 17

Data from Figure 2b

10.17182/hepdata.91129.v1/t17

Amplitudes of the radii oscillations as function of centrality percentile for four different $k_{\mathrm{T}}$.

• #### Table 18

Data from Figure 2b

10.17182/hepdata.91129.v1/t18

Amplitudes of the radii oscillations as function of centrality percentile for four different $k_{\mathrm{T}}$.

• #### Table 19

Data from Figure 2b

10.17182/hepdata.91129.v1/t19

Amplitudes of the radii oscillations as function of centrality percentile for four different $k_{\mathrm{T}}$.

• #### Table 20

Data from Figure 2b

10.17182/hepdata.91129.v1/t20

Amplitudes of the radii oscillations as function of centrality percentile for four different $k_{\mathrm{T}}$.

• #### Table 21

Data from Figure 2c

10.17182/hepdata.91129.v1/t21

Amplitudes of the radii oscillations as function of centrality percentile for four different $k_{\mathrm{T}}$.

• #### Table 22

Data from Figure 2c

10.17182/hepdata.91129.v1/t22

Amplitudes of the radii oscillations as function of centrality percentile for four different $k_{\mathrm{T}}$.

• #### Table 23

Data from Figure 2c

10.17182/hepdata.91129.v1/t23

Amplitudes of the radii oscillations as function of centrality percentile for four different $k_{\mathrm{T}}$.

• #### Table 24

Data from Figure 2c

10.17182/hepdata.91129.v1/t24

Amplitudes of the radii oscillations as function of centrality percentile for four different $k_{\mathrm{T}}$.

• #### Table 25

Data from Figure 2d

10.17182/hepdata.91129.v1/t25

Amplitudes of the radii oscillations as function of centrality percentile for four different $k_{\mathrm{T}}$.

• #### Table 26

Data from Figure 2d

10.17182/hepdata.91129.v1/t26

Amplitudes of the radii oscillations as function of centrality percentile for four different $k_{\mathrm{T}}$.

• #### Table 27

Data from Figure 2d

10.17182/hepdata.91129.v1/t27

Amplitudes of the radii oscillations as function of centrality percentile for four different $k_{\mathrm{T}}$.

• #### Table 28

Data from Figure 2d

10.17182/hepdata.91129.v1/t28

Amplitudes of the radii oscillations as function of centrality percentile for four different $k_{\mathrm{T}}$.

• #### Table 29

Data from Figure 3a

10.17182/hepdata.91129.v1/t29

Amplitudes of the relative radii oscillations as function of centrality percentile for four different $k_{\mathrm{T}}$.

• #### Table 30

Data from Figure 3a

10.17182/hepdata.91129.v1/t30

Amplitudes of the relative radii oscillations as function of centrality percentile for four different $k_{\mathrm{T}}$.

• #### Table 31

Data from Figure 3a

10.17182/hepdata.91129.v1/t31

Amplitudes of the relative radii oscillations as function of centrality percentile for four different $k_{\mathrm{T}}$.

• #### Table 32

Data from Figure 3a

10.17182/hepdata.91129.v1/t32

Amplitudes of the relative radii oscillations as function of centrality percentile for four different $k_{\mathrm{T}}$.

• #### Table 33

Data from Figure 3b

10.17182/hepdata.91129.v1/t33

Amplitudes of the relative radii oscillations as function of centrality percentile for four different $k_{\mathrm{T}}$.

• #### Table 34

Data from Figure 3b

10.17182/hepdata.91129.v1/t34

Amplitudes of the relative radii oscillations as function of centrality percentile for four different $k_{\mathrm{T}}$.

• #### Table 35

Data from Figure 3b

10.17182/hepdata.91129.v1/t35

Amplitudes of the relative radii oscillations as function of centrality percentile for four different $k_{\mathrm{T}}$.

• #### Table 36

Data from Figure 3b

10.17182/hepdata.91129.v1/t36

Amplitudes of the relative radii oscillations as function of centrality percentile for four different $k_{\mathrm{T}}$.

• #### Table 37

Data from Figure 3c

10.17182/hepdata.91129.v1/t37

Amplitudes of the relative radii oscillations as function of centrality percentile for four different $k_{\mathrm{T}}$.

• #### Table 38

Data from Figure 3c

10.17182/hepdata.91129.v1/t38

Amplitudes of the relative radii oscillations as function of centrality percentile for four different $k_{\mathrm{T}}$.

• #### Table 39

Data from Figure 3c

10.17182/hepdata.91129.v1/t39

Amplitudes of the relative radii oscillations as function of centrality percentile for four different $k_{\mathrm{T}}$.

• #### Table 40

Data from Figure 3c

10.17182/hepdata.91129.v1/t40

Amplitudes of the relative radii oscillations as function of centrality percentile for four different $k_{\mathrm{T}}$.

• #### Table 41

Data from Figure 4

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The relative amplitudes of the radius oscillations dependence on the third-order anisotropies in space and transverse flow for kT =...

• #### Table 42

Data from Figure 4

10.17182/hepdata.91129.v1/t42

The relative amplitudes of the radius oscillations dependence on the third-order anisotropies in space and transverse flow for kT =...

• #### Table 43

Data from Figure 4

10.17182/hepdata.91129.v1/t43

Blast-Wave model source parameters, final source anisotropy ($a_{3}$) and transverse flow ($\rho_{3}$);, for different centrality ranges, as obtained from the...

• #### Table 44

Data from Figure 4

10.17182/hepdata.91129.v1/t44

Blast-Wave model source parameters, final source anisotropy ($a_{3}$) and transverse flow ($\rho_{3}$);, for different centrality ranges, as obtained from the...

• #### Table 45

Data from Figure 4

10.17182/hepdata.91129.v1/t45

Blast-Wave model source parameters, final source anisotropy ($a_{3}$) and transverse flow ($\rho_{3}$);, for different centrality ranges, as obtained from the...

• #### Table 46

Data from Figure 4

10.17182/hepdata.91129.v1/t46

Blast-Wave model source parameters, final source anisotropy ($a_{3}$) and transverse flow ($\rho_{3}$);, for different centrality ranges, as obtained from the...

• #### Table 47

Data from Figure 4

10.17182/hepdata.91129.v1/t47

Blast-Wave model source parameters, final source anisotropy ($a_{3}$) and transverse flow ($\rho_{3}$), for different centrality ranges, as obtained from the...

• #### Table 48

Data from Figure 4

10.17182/hepdata.91129.v1/t48

Blast-Wave model source parameters, final source anisotropy ($a_{3}$) and transverse flow ($\rho_{3}$), for different centrality ranges, as obtained from the...