Studying the jet medium interaction by two particle Δη–Δϕ correlations

We present two-dimensional Δη–Δϕ inclusive photon-charged hadron correlations measured by the PHENIX experiment. Jet-like correlations are modified in central Au + Au collisions compared to image collisions, in both the trigger jet and opposing jet. The trigger jet is elongated in pseudo-rapidity (the “ridge”), while the opposing jet shows a double peak structure (“head” and “shoulder”). We decompose the structures by fitting the Δη and Δϕ correlations to disentangle components from the medium, the punch-through and the trigger jets. The ridge exists for associated particle image below image; it is broad in rapidity and narrow in Δϕ. The away side correlated particle yield is enhanced in central collisions. The yield of the ridge closely resembles the shoulder in the centrality dependence of particle yield and spectra.