Most Wanted: Chiral Magnetic Effect

Gauge fields provide the fundamental interactions in the Standard Model of particle physics. Gauge field configurations with nontrivial topological windings are known to play crucial roles in many important phenomena, from matter-anti-matter asymmetry of today's universe and the permanent quark confinement to topological phases in condensed matter. Their presence is however elusive for direct detection in experiments. It turns out that measurements of the so-called chiral magnetic effect (CME) in heavy ion collisions can be used to access and manifest gauge field topology. The CME is a nontrivial macroscopic transport process arising from microscopic quantum anomaly of underlying chiral fermions in a chiral material (e.g. a Dirac/Weyl semimetal or a quark-gluon plasma), which has been in the spotlight lately across disciplines of physics. Potential discovery of CME in heavy ion collisions is of utmost significance, with extensive experimental searches carried out over the past decade. Some twelve years after the first hint of a possible CME signal, excitement has been mounting on a key experiment: the isobar collisions at the Relativistic Heavy Ion Collider (RHIC). With the first isobar run analysis results just released, this talk will evaluate the key implications of this initial message for the CME search and discuss important issues to be further addressed with near-term theoretical/experimental efforts in order to draw a convincing interpretation from the rich isobar dataset.