Charge conservation at energies available at the BNL Relativistic Heavy Ion Collider and contributions to local parity violation observables

Abstract

Relativistic heavy ion collisions provide laboratory environments from which one can study the creation of a novel state of matter, the quark-gluon plasma. The existence of such a state is postulated to alter the mechanism and evolution of charge production, which then becomes manifest in charge correlations. We study the separation of balancing charges at kinetic freeze-out by analyzing recent results on balancing charge correlations for Au + Au collisions at $\sqrt{{s}_{\mathrm{NN}}}=200 \text{GeV}$. We find that in central collisions, the spatial points from which balancing charges are emitted are characterized by smaller relative angles. These results are consistent with the expectation that charge production occurred later in the collision, as would be expected for delayed hadronization. An alternative explanation would be that the charges were produced early, perhaps with a different mechanism where the charge production mechanism was altered from string breaking which tends to separate the charges in relative rapidity. The alternative explanation would also rely on the diffusion of charges being small. In addition we calculate the contributions from charge-balance correlations to STAR's local parity violation observable. We find that local charge conservation, when combined with elliptic flow, explains the bulk of STAR's measurement.