On the origin of trigger-angle dependence of di-hadron correlations

The STAR Collaboration reported measurements of di-hadron azimuthal correlation in medium-central Au+Au collisions at 200 A$\,$GeV, where the data are presented as a function of the trigger particle's azimuthal angle relative to the event plane $ϕ_s$. In particular, it is observed that the away-side correlation evolves from single- to double-peak structure with increasing $ϕ_s$. In this work, we present the calculated correlations as functions of both $ϕ_s$ and particle transverse momentum $p_T$, using the hydrodynamic code NeXSPheRIO. The results are found to be in reasonable agreement with the STAR data. We further argue that the above $ϕ_s$ dependence of the correlation structure can be understood in terms of one-tube model, as due to an interplay between the background elliptic flow caused by the initial state global geometry and the flow produced by fluctuations.

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