Charge separation measurements in Au+Au collisions at = 7.7−200 GeV in search of the chiral magnetic effect*

The chiral magnetic effect in heavy-ion collisions predicts an electric charge separation along the direction of a strong magnetic field, which indicates local parity ( ) and charge-conjugation-parity ( ) violation in strong interactions. We report measurements of electric charge separation signals perpendicular to the spectator event plane in Au+Au collisions using high-statistics data from RHIC Beam Energy Scan II and top-RHIC energy ( GeV) runs. A novel event shape selection method is employed to suppress the flow-induced background. The residual charge-separation signal fractions near the zero-flow limit are positive in Au+Au collisions within the 20%−50% centrality range. The significance levels are , , and at 11.5, 14.6, and 19.6 GeV, respectively. At other beam energies, the signals are either statistically limited or consistent with zero.