Search for the Chiral Magnetic Effect with charge-dependent azimuthal correlations in Xe-Xe collisions at $\sqrt{s_{\mathrm{NN}}} = 5.44$ TeV

The ALICE collaboration
Phys.Lett.B 856 (2024) 138862, 2024.

Abstract (data abstract)
Charge-dependent two- and three-particle correlations measured in Xe-Xe collisions at $\sqrt{s_{\mathrm{NN}}} = 5.44$ TeV are presented. Results are obtained for charged particles in the pseudorapidity range $|\eta|<0.8$ and transverse momentum interval $0.2 \le p_{\rm T} < 5.0$ GeV/$c$ for different collision centralities. The three-particle correlator $\gamma_{\alpha\beta} \equiv \langle \cos(\varphi_\alpha + \varphi_\beta - 2\Psi_2) \rangle$, calculated for different combinations of charge sign $\alpha$ and $\beta$, is expected to be sensitive to the presence of the Chiral Magnetic Effect (CME). Its magnitude is similar to the one observed in Pb-Pb collisions in contrast to a smaller CME signal in Xe-Xe collisions than in Pb-Pb collisions predicted by Monte Carlo (MC) calculations including a magnetic field induced by the spectator protons. These observations point to a large non-CME contribution to the correlator. Furthermore, the charge dependence of $\gamma_{\alpha\beta}$ can be described by a blast wave model calculation that incorporates background effects and by the Anomalous Viscous Fluid Dynamics model with values of the CME signal consistent with zero. The Xe-Xe and Pb-Pb results are combined with the expected CME signal dependence on the system size from the MC calculations including a magnetic field to obtain the fraction of CME contribution in $\gamma_{\alpha\beta}$, $f_{\rm CME}$. The CME fraction is compatible with zero for the most 30% central events in both systems and then becomes positive; averaging over the 0-70% centrality interval yields an upper limit of 2% (3%) and 25% (32%) at 95% (99.7%) confidence level for the CME signal contribution to $\gamma_{\alpha\beta}$ in Xe-Xe and Pb-Pb collisions, respectively.

  • Table 1

    Data from Fig 1.

    10.17182/hepdata.153409.v1/t1

    $\langle \cos(\varphi_{\alpha} - \varphi_{\beta}) \rangle$ (opposite charge pairs) as a function of centrality in Xe-Xe collisions at $\sqrt{s_{\rm NN}} =...

  • Table 2

    Data from Fig 1.

    10.17182/hepdata.153409.v1/t2

    $\langle \cos(\varphi_{\alpha} - \varphi_{\beta}) \rangle$ (same charge pairs) as a function of centrality in Xe-Xe collisions at $\sqrt{s_{\rm NN}} =...

  • Table 3

    Data from Fig 1.

    10.17182/hepdata.153409.v1/t3

    $\langle \cos(\varphi_{\alpha} + \varphi_{\beta} - 2\Psi_{2}) \rangle$ (opposite charge pairs) as a function of centrality in Xe-Xe collisions at $\sqrt{s_{\rm...

  • Table 4

    Data from Fig 1.

    10.17182/hepdata.153409.v1/t4

    $\langle \cos(\varphi_{\alpha} + \varphi_{\beta} - 2\Psi_{2}) \rangle$ (same charge pairs) as a function of centrality in Xe-Xe collisions at $\sqrt{s_{\rm...

  • Table 5

    Data from Fig 2.

    10.17182/hepdata.153409.v1/t5

    $\langle \cos(\varphi_{\alpha} + \varphi_{\beta} - 2\Psi_{2}) \rangle$ (opposite charge pairs) as a function of pseudorapidity difference $|\eta_{\alpha}-\eta_{\beta}|$ in 20-30% Xe-Xe...

  • Table 6

    Data from Fig 2.

    10.17182/hepdata.153409.v1/t6

    $\langle \cos(\varphi_{\alpha} + \varphi_{\beta} - 2\Psi_{2}) \rangle$ (same charge pairs) as a function of pseudorapidity difference $|\eta_{\alpha}-\eta_{\beta}|$ in 20-30% Xe-Xe...

  • Table 7

    Data from Fig 2.

    10.17182/hepdata.153409.v1/t7

    $\langle \cos(\varphi_{\alpha} + \varphi_{\beta} - 2\Psi_{2}) \rangle$ (opposite charge pairs) as a function of transverse momentum difference $|p_{\rm T_{\alpha}}-p_{\rm T_{\beta}}|$...

  • Table 8

    Data from Fig 2.

    10.17182/hepdata.153409.v1/t8

    $\langle \cos(\varphi_{\alpha} + \varphi_{\beta} - 2\Psi_{2}) \rangle$ (same charge pairs) as a function of transverse momentum difference $|p_{\rm T_{\alpha}}-p_{\rm T_{\beta}}|$...

  • Table 9

    Data from Fig 2.

    10.17182/hepdata.153409.v1/t9

    $\langle \cos(\varphi_{\alpha} + \varphi_{\beta} - 2\Psi_{2}) \rangle$ (opposite charge pairs) as a function of average transverse momentum $(p_{\rm T_{\alpha}}+p_{\rm T_{\beta}})/2$...

  • Table 10

    Data from Fig 2.

    10.17182/hepdata.153409.v1/t10

    $\langle \cos(\varphi_{\alpha} + \varphi_{\beta} - 2\Psi_{2}) \rangle$ (same charge pairs) as a function of average transverse momentum $(p_{\rm T_{\alpha}}+p_{\rm T_{\beta}})/2$...

  • Table 11

    Data from Fig 3.

    10.17182/hepdata.153409.v1/t11

    $\langle \cos(\varphi_{\alpha} - \varphi_{\beta}) \rangle$ (opposite-same charge pairs) as a function of centrality in Xe-Xe collisions at $\sqrt{s_{\rm NN}} =...

  • Table 12

    Data from Fig 3.

    10.17182/hepdata.153409.v1/t12

    $\langle \cos(\varphi_{\alpha} + \varphi_{\beta} - 2\Psi_{2}) \rangle$ (opposite-same charge pairs) as a function of centrality in Xe-Xe collisions at $\sqrt{s_{\rm...

  • Table 13

    Data from Fig 6.

    10.17182/hepdata.153409.v1/t13

    CME fraction extracted using B from MC Glauber model as a function of centrality in Xe-Xe collisions at $\sqrt{s_{\rm NN}}...

  • Table 14

    Data from Fig 6.

    10.17182/hepdata.153409.v1/t14

    CME fraction extracted using B from T$_{\rm R}$ENTo model as a function of centrality in Xe-Xe collisions at $\sqrt{s_{\rm NN}}...

  • Table 15

    Data from Fig 6.

    10.17182/hepdata.153409.v1/t15

    CME fraction extracted using B from MC Glauber model as a function of centrality in Pb-Pb collisions at $\sqrt{s_{\rm NN}}...

  • Table 16

    Data from Fig 6.

    10.17182/hepdata.153409.v1/t16

    CME fraction extracted using B from T$_{\rm R}$ENTo model as a function of centrality in Pb-Pb collisions at $\sqrt{s_{\rm NN}}...

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