Observation of Charge-Dependent Azimuthal Correlations in p−Pb Collisions and Its Implication for the Search for the Chiral Magnetic Effect

TLDR: The observed differences between the same and opposite sign correlations, as functions of multiplicity and η gap between the two charged particles, are of similar magnitude in p-Pb and PbPb collisions at the same multiplicities.

Abstract: Charge-dependent azimuthal particle correlations with respect to the second-order event plane in pPb and PbPb collisions at a nucleon-nucleon center-of-mass energy of 5.02 TeV have been studied with the CMS experiment at the LHC. The measurement is performed with a three-particle correlation technique, using two particles with the same or opposite charge within the pseudorapidity range abs(eta)<2.4, and a third particle measured in the hadron forward calorimeters (4.4< abs(eta)<5). The observed differences between the same and opposite sign correlations, as functions of multiplicity and eta gap between the two charged particles, are of similar magnitude in pPb and PbPb collisions at the same multiplicities. These results pose a challenge for the interpretation of charge-dependent azimuthal correlations in heavy ion collisions in terms of the chiral magnetic effect.