Charge Independent(CI) and Charge Dependent(CD) correlations vs. Centrality from $\Delta \phi \Delta \eta$ Charged Pairs in Minimum Bias Au + Au Collisions at 200 Gev

Abstract

We report high precision charged-particle pair (2-D) correlation analyses in the space of $\Delta \phi$ (azimuth) and $\Delta \eta$ (pseudorapidity), for minimum bias Au + Au collisions at $\sqrt{s_{NN}}$ = 200 GeV as a function of centrality (0-80%). The intermediate transverse momenta region chosen $0.8 < p_t < 4.0$ GeV/c corresponds to an emission source size $\sim2$fm obtained from HBT measurements and should resolve substructures at the scale of $\sim2$fm. The difference and the sum of unlike-sign and like-sign charged pairs form Charge Dependent (CD) correlations and Charge Independent (CI) correlations respectively. The CD displays the initial correlation at hadronization of the opposite sign pairs emitted from the same space-time region as modified by further medium interactions before kinetic freeze-out. Our analysis of the CD correlations shows approximately jet-like structure, independent of centrality and is consistent with the initial correlation which is predicted by Pythia (or HIJING) jets. The CI correlation displays the average structure of the correlated emitting sources after kinetic freeze-out. For the most central bins, the $\Delta \eta$ width of the CI correlation on the near side ($\Delta \phi$ around $0^\circ$) is elongated by a factor $\sim$3 destroying the jet-like symmetry. This elongation decreases continually with decreasing centrality and essentially restores the jet-like symmetric structure in the most peripheral bins. The Pythia and HIJING event generators together with a QCD inspired Parton Bubble Model (PBM), which motivated this analysis, are used to compare to our data. We discuss the arguments for substructure, surface emission, and opacity in the central fireball region.