Observation of charge-dependent azimuthal correlations in pPb collisions and its implication for the search for the chiral magnetic effect

TL;DR

This study measures charge-dependent azimuthal correlations in pPb and PbPb collisions at 5.02 TeV, revealing similarities that challenge the interpretation of these correlations as evidence of the chiral magnetic effect.

Contribution

It provides the first detailed comparison of charge-dependent correlations in pPb and PbPb collisions, questioning the assumption that such correlations are solely due to the chiral magnetic effect.

Findings

Similar magnitude of charge-dependent correlations in pPb and PbPb collisions.

Results challenge the interpretation of correlations as evidence for the chiral magnetic effect.

Measurement performed with a three-particle correlation technique.

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.