To CME or not to CME? Implications of p+Pb measurements of the chiral magnetic effect in heavy ion collisions

Understand

The Chiral Magnetic Effect (CME) is a fundamental prediction of QCD, and various observables have been proposed in heavy ion collisions to access this physics.

• Recently the CMS Collaboration \cite{Khachatryan:2016got} has reported results from p+Pb collisions at 5.02 TeV on one such observable, the three-point correlator.
• The results are strikingly similar to those measured at the same particle multiplicity in Pb+Pb collisions, which have been attributed to the CME.
• This similarity, combined with two key assumptions about the magnetic field in p+Pb collisions, presents a major challenge to the CME picture.