Evidence for Color Transparency and Direct Hadron Production at RHIC

The QCD color transparency of higher-twist contributions to the inclusive hadroproduction cross section, where the trigger proton is produced directly in a short-distance subprocess, can explain several remarkable features of high-pT proton production in heavy ion collisions which have recently been observed at RHIC: (a) the anomalous increase of the p → π ratio with centrality (b): the more rapid power-law fall-off at fixed xT = 2pT/√s of the charged particle production cross section in high centrality nuclear collisions, and (c): the anomalous decrease of the number of same-side hadrons produced in association with a proton trigger as the centrality increases. These phenomena illustrate how heavy ion collisions can provide sensitive tools for interpreting and testing fundamental properties of QCD