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Constraining the Chiral Magnetic Effect with charge-dependent azimuthal correlations in Pb-Pb collisions at $ \sqrt{s_{\mathrm{NN}}} $ = 2.76 and 5.02 TeV

The ALICE collaboration
JHEP 09 (2020) 160, 2020.

Abstract (data abstract)
"Systematic studies of charge-dependent two- and three-particle correlations in Pb--Pb collisions at $\sqrt{\it{s}_\mathrm{{NN}}} = $ 2.76~and 5.02~TeV used to probe the Chiral Magnetic Effect (CME) are presented. These measurements are performed for charged particles in the pseudorapidity ($\eta$) and transverse momentum ($p_{\rm{T}}$) ranges $\left|\eta \right| < 0.8$ and $0.2 < p_{\mathrm{T}} < 5$~GeV/$c$. A significant charge-dependent signal that becomes more pronounced for peripheral collisions is reported for the CME-sensitive correlators $\gamma_{1,1} = \langle \cos (\varphi_{\alpha} +\varphi_{\beta} - 2\Psi_{2}) \rangle$ and $\gamma_{1,-3} = \langle \cos (\varphi_{\alpha} -3\varphi_{\beta} + 2\Psi_{2}) \rangle$. The results are used to estimate the contribution of background effects, associated with local charge conservation coupled to anisotropic flow modulations, to measurements of the CME. A blast-wave parametrisation that incorporates local charge conservation tuned to reproduce the centrality dependent background effects is not able to fully describe the measured $\gamma_{1,1}$. Finally, the charge and centrality dependence of mixed-harmonics three-particle correlations, of the form $\gamma_{1,2} = \langle \cos (\varphi_{\alpha} + 2 \varphi_{\beta} - 3\Psi_{3}) \rangle$, which are insensitive to the CME signal, verify again that background contributions dominate the measurement of $\gamma_{1,1}$."

  • Table 1

    Figure 1


    2-particle integrated correlators

  • Table 2

    Figure 2 left column


    2-particle differential correlator versus pT difference

  • Table 3

    Figure 2 middle column


    2-particle differential correlator versus average pT

  • Table 4

    Figure 2 right column


    2-particle differential correlator versus eta difference

  • Table 5

    Figure 3


    3-particle integrated correlators

  • Table 6

    Figure 4 left column


    3-particle differential correlator versus pT difference

  • Table 7

    Figure 4 left column


    3-particle differential correlator versus average pT

  • Table 8

    Figure 4 left column


    3-particle differential correlator versus eta difference

  • Table 9

    Figure 5


    3-particle differential correlator OS - SS

  • Table 10

    Figure 8, left panel


    CME fraction

  • Table 11

    Figure 8, right panel


    CME fraction

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