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

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Abstract

<jats:title>A<jats:sc>bstract</jats:sc> </jats:title><jats:p>Systematic studies of charge-dependent two- and three-particle correlations in Pb-Pb collisions at <jats:inline-formula><jats:alternatives><jats:tex-math>$$ \sqrt{s_{\mathrm{NN}}} $$</jats:tex-math><mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msqrt> <mml:msub> <mml:mi>s</mml:mi> <mml:mi>NN</mml:mi> </mml:msub> </mml:msqrt> </mml:math></jats:alternatives></jats:inline-formula> = 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 (<jats:italic>η</jats:italic>) and transverse momentum (<jats:italic>p</jats:italic><jats:sub>T</jats:sub>) ranges |<jats:italic>η</jats:italic>| <jats:italic><</jats:italic> 0<jats:italic>.</jats:italic>8 and 0<jats:italic>.</jats:italic>2 <jats:italic>< p</jats:italic><jats:sub>T</jats:sub><jats:italic><</jats:italic> 5 GeV/<jats:italic>c</jats:italic>. A significant charge-dependent signal that becomes more pronounced for peripheral collisions is reported for the CME-sensitive correlators <jats:italic>γ</jats:italic><jats:sub>1, 1</jats:sub> = ⟨cos(<jats:italic>φ</jats:italic><jats:sub><jats:italic>α</jats:italic></jats:sub> + <jats:italic>φ</jats:italic><jats:sub><jats:italic>β</jats:italic></jats:sub> − 2Ψ<jats:sub>2</jats:sub>)⟩ and <jats:italic>γ</jats:italic><jats:sub>1, − 3</jats:sub> = ⟨cos(<jats:italic>φ</jats:italic><jats:sub><jats:italic>α</jats:italic></jats:sub> − 3<jats:italic>φ</jats:italic><jats:sub><jats:italic>β</jats:italic></jats:sub> + 2Ψ<jats:sub>2</jats:sub>)⟩. 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 <jats:italic>γ</jats:italic><jats:sub>1<jats:italic>,</jats:italic>1</jats:sub>. Finally, the charge and centrality dependence of mixed-harmonics three-particle correlations, of the form <jats:italic>γ</jats:italic><jats:sub>1, 2</jats:sub> = ⟨cos(<jats:italic>φ</jats:italic><jats:sub><jats:italic>α</jats:italic></jats:sub> + 2<jats:italic>φ</jats:italic><jats:sub><jats:italic>β</jats:italic></jats:sub> − 3Ψ<jats:sub>3</jats:sub>)⟩, which are insensitive to the CME signal, verify again that background contributions dominate the measurement of <jats:italic>γ</jats:italic><jats:sub>1<jats:italic>,</jats:italic>1</jats:sub>.</jats:p>

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