Di-hadron correlations at RHIC

Di-hadron correlations have been used to study jets at RHIC and have yielded rich insight into the properties of the medium. Studies show that the near-side peak of high-pT triggered correlations can be decomposed into two parts, a jet-like correlation and the ridge. The jet-like correlation is narrow in both azimuth and pseudorapidity and has properties consistent with vacuum fragmentation, while the ridge is narrow in azimuth but broad in pseudorapidity and roughly independent of pseudorapidity. The energy, system, and particle composition of the jet -like correlation and the ridge are discussed. Data indicate that the jet-like correlation is dominantly produced by vacuum fragmentation. Attempts have been made to explain the production of the ridge component as coming from recombination, momentum kicks, and QCD magnetic fields. However, few models have attempted to quantitatively calculate the characteristics of the ridge. The wealth of data should help distinguish models for the production mechanism of the ridge. Implications for studies of the jet-like correlation and the ridge at the Lhc are discussed.