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

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 $0.2\le p_{\mathrm{T}}<5.0$ GeV/$c$ for different collision centralities. The three-particle correlator ${\gamma }_{\alpha \beta }\equiv ⟨\cos ({\phi }_{\alpha }+{\phi }_{\beta }-2{\Psi }_2)⟩$, 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 ${\gamma }_{\alpha \beta }$, $f_{\mathrm{CME}}$. The CME fraction is compatible with zero for the 30% most central events in both systems and then becomes positive. This 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 the 0-70% Xe-Xe and Pb-Pb collisions, respectively.

arXiv comment23 pages, 6 captioned figures, 1 table, authors from page 18, published version, figures at http://alice-publications.web.cern.ch/node/8595

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