Overview of the Experimental Results on the CME signal

The chiral magnetic effect (CME) is predicted to occur as a consequence of local parity violation of the strong interaction under a strong electro-magnetic field generated in relativistic heavy-ion collisions. The existence of CME would be the manifestation of a fundamental structure of QCD vacuum --- its topological fluctuation. The experimental signal for CME involves a separation of positively and negatively charged hadrons along the direction of the magnetic field. The search for the CME in relativistic heavy ion collisions has been carried out over the past decade, and is usually complicated by various backgrounds which also contribute to the charge separation. To better control the influence of signal and backgrounds, the STAR collaboration at RHIC performed a highly anticipated analysis of isobar collisions. In this talk I will review previous measurements at both RHIC and LHC, and in particular I will discuss the result from isobar collisions that was recently reported by the STAR collaboration. I will also discuss the implication of our current results on future search efforts.