The baryon anomaly: Evidence for color transparency and direct hadron production at RHIC

We show that the QCD color transparency of higher-twist contributions to inclusive hadroproduction cross sections, where baryons are produced directly in a short-distance subprocess, can explain several remarkable features of high-pTpT baryon production in heavy ion collisions which have recently been observed at RHIC: (a) the anomalous increase of the proton-to-pion ratio with centrality, (b) the increased 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. We show that correlations between opposite-side hyperons and kaons can provide a clear signature of higher-twist contributions. These phenomena emphasize the importance of understanding hadronization at the amplitude level in QCD illustrate how heavy ion collisions can provide sensitive tools for interpreting and testing fundamental properties of QCD.