Hydrodynamic approach to the centrality dependence of di-hadron correlations

Measurements of di-hadron azimuthal correlations at different centralities for Au+Au collisions at $200A$ GeV were reported by the PHENIX Collaboration. The data were presented for different ranges of transverse momentum. In particular, it was observed that the away-side correlation evolves from a double- to a single-peak structure when the centrality decreases. In this work, we show that these features naturally appear due to an interplay between the centrality-dependent smooth background elliptic flow and the one produced by event-by-event fluctuating peripheral tubes. To compare with the PHENIX data, we also carry out numerical simulations by using a hydrodynamical code nexspherio, and calculate the correlations by both cumulant and the ZYAM method employed by the PHENIX Collaboration. Our results are in reasonable agreement with the data. A brief discussion on the physical content of the present model and its difference from other viewpoints is also presented.

Figure 1

Di-hadron correlations calculated by the cumulant method. The calculations are done by using the parameters in Eq. (8), the correlation is normalized by the number of particles. (a) The tube contribution; (b) the one from the background (dashed line) and the resultant correlation (solid line) for central collisions, as given by Eq. (7); and (c) the corresponding ones for the peripheral collisions.

Figure 2

Subtracted di-hadron correlations as a function of $\mathrm{\Delta }\varphi$ for different centrality windows and $p_T^a$ range for $200A$ GeV Au+Au collisions. nexspherio results in solid curves are compared with PHENIX data in filled circles.

Figure 3

Same as Fig. 2, but obtained by using the ZYAM method.