Addressing the physics of the ridge by 2- and 3-particle correlations at STAR Original Research Article

We present new results on 2-particle azimuthal (Δϕ) correlation relative to event plane and 3-particle pseudorapidity (Δη) correlation at mid-rapidity in Au+Au collisions at View the MathML source, measured by the STAR experiment. While jet-like correlation is symmetric, ridge is found to be asymmetric when trigger particle azimuth is between in- and out-of-plane. The charge ordering properties between associated and trigger particles are exploited to separate jet-like and ridge contributions in 3-particle Δη-Δη correlations. We found that like-sign triplets are dominated by ridge. The separated ridge, while narrow in Δϕ, is extremely broad in Δη. The ridge particles are not only uncorrelated to the trigger particle in Δη, but also uncorrelated between themselves.