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

Abstract

Systematic studies of charge-dependent two- and three-particle correlations in Pb-Pb collisions at $\sqrt{s_{\mathrm{NN}}}=$ 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 ($p_{\mathrm{T}}$) 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 ${\gamma }_{1,1}=⟨\cos ({\phi }_{\alpha }+{\phi }_{\beta }-2{\Psi }_2)⟩$ and ${\gamma }_{1,-3}=⟨\cos ({\phi }_{\alpha }-3{\phi }_{\beta }+2{\Psi }_2)⟩$. 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 ${\gamma }_{1,2}=⟨\cos ({\phi }_{\alpha }+2{\phi }_{\beta }-3{\Psi }_3)⟩$, which are insensitive to the CME signal, verify again that background contributions dominate the measurement of ${\gamma }_{1,1}$.

29 pages, 8 captioned figures, 4 tables, authors from page 24, published version, figures at http://alice-publications.web.cern.ch/node/6296

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• The Chiral Magnetic Effect
• The QCD equation of state with dynamical quarks
• Charge separation induced by P-odd bubbles in QCD matter
• Triangular flow in hydrodynamics and transport theory
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• Charge conservation in RHIC and contributiuons to local parity violation observables
• Elliptic flow in the Gaussian model of eccentricity fluctuations
• Observation of charge-dependent azimuthal correlations in pPb collisions and its implication for the search for the chiral magnetic effect
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