Search for the Chiral Magnetic Effect with the ALICE detector

Abstract

In non-central heavy-ion collisions, spectator protons that do not participate in the interaction create strong magnetic fields. The strength of these fields allows testing an effect based on the hypothesized properties of QCD. The presence of so-called topological configurations can give rise to domains that carry net chirality. Coupled with the aforementioned magnetic fields, they may induce a charge separation of the particles generated in the collisions. This charge separation is called the Chiral Magnetic Effect (CME) and can be measured through charged-particle angular correlations. Measurements of the γ1,1 correlator, which is sensitive to the CME, are shown for Pb–Pb collisions at sNN=5.02TeV as well as for Xe–Xe collisions at sNN=5.44TeV. These are found to have a significant charge dependence between opposite-sign and same-sign charge pairs. This behavior is consistent with a CME-like signal. However, the δ1 correlator, which measures charge correlations unrelated to any symmetry plane (i.e. background), was measured in Xe–Xe collisions and also shows a significant charge dependence. This prevents a clear interpretation of the γ1,1 correlator. Novel methods to constrain the CME contribution to the γ1,1 correlator are necessary.