# Azimuthal anisotropy of charged particles with transverse momentum up to 100 GeV/c in PbPb collisions at $\sqrt{s_{NN}}$ = 5.02 TeV

## Abstract

The Fourier coefficients$\upsilon_2$ and $\upsilon_3$ characterizing the anisotropy of the azimuthal distribution of charged particles produced in PbPb collisions at $\sqrt{s_{NN}}$ = 5.02 TeV are measured with data collected by the CMS experiment. The measurements cover a broad transverse momentum range, $1 < p_T<100GeV/c$. The analysis focuses on the $p_T > 10GeV/c$ range, where anisotropic azimuthal distributions should reflect the path-length dependence of parton energy loss in the created medium. Results are presented in several bins of PbPb collision centrality, spanning the 60% most central events. The $\upsilon_2$ coefficient is measured with the scalar product and the multiparticle cumulant methods, which have different sensitivities to initial-state fluctuations. The values from both methods remain positive up to $p_T \sim 60–80GeV/c$, in all examined centrality classes. The $\upsilon_3$ coefficient, only measured with the scalar product method, tends to zero for $p_T \gtrsim 20GeV/c$. Comparisons between theoretical calculations and data provide new constraints on the path-length dependence of parton energy loss in heavy ion collisions and highlight the importance of the initial-state fluctuations.

## Abstract

The Fourier coefficients$\upsilon_2$ and $\upsilon_3$ characterizing the anisotropy of the azimuthal distribution of charged particles produced in PbPb collisions at $\sqrt{s_{NN}}$ = 5.02 TeV are measured with data collected by the CMS experiment. The measurements cover a broad transverse momentum range, $1 < p_T<100GeV/c$. The analysis focuses on the $p_T > 10GeV/c$ range, where anisotropic azimuthal distributions should reflect the path-length dependence of parton energy loss in the created medium. Results are presented in several bins of PbPb collision centrality, spanning the 60% most central events. The $\upsilon_2$ coefficient is measured with the scalar product and the multiparticle cumulant methods, which have different sensitivities to initial-state fluctuations. The values from both methods remain positive up to $p_T \sim 60–80GeV/c$, in all examined centrality classes. The $\upsilon_3$ coefficient, only measured with the scalar product method, tends to zero for $p_T \gtrsim 20GeV/c$. Comparisons between theoretical calculations and data provide new constraints on the path-length dependence of parton energy loss in heavy ion collisions and highlight the importance of the initial-state fluctuations.

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