Event-plane dependent dihadron correlations with harmonic $v_n$ subtraction in Au+Au Collisions at $\sqrt{s_{_{\rm NN}}}=200$ GeV

Abstract

STAR measurements of dihadron azimuthal correlations ($Δϕ$) are reported in mid-central (20-60\%) Au+Au collisions at $\sqrt{s_{_{\rm NN}}}=200$ GeV as a function of the trigger particle's azimuthal angle relative to the event plane, $ϕ_{s}=|ϕ_{t}-ψ_{\rm EP}|$. The elliptic ($v_2$), triangular ($v_3$), and quadratic ($v_4$) flow harmonic backgrounds are subtracted using the Zero Yield At Minimum (ZYAM) method. The results are compared to minimum-bias d+Au collisions. It is found that a finite near-side ($|Δϕ|<π/2$) long-range pseudorapidity correlation (ridge) is present in the in-plane direction ($ϕ_{s}\sim 0$). The away-side ($|Δϕ|>π/2$) correlation shows a modification from d+Au data, varying with $ϕ_{s}$. The modification may be a consequence of pathlength-dependent jet-quenching and may lead to a better understanding of high-density QCD.