The Baryon Anomaly: Evidence for Color Transparency and Direct Hadron Production at RHIC

TL;DR

This paper demonstrates that color transparency and direct hadron production in QCD can explain several unexpected features observed in high-$p_T$ baryon production at RHIC, shedding light on hadronization processes in heavy ion collisions.

Contribution

It introduces the role of higher-twist contributions and color transparency in explaining RHIC baryon production anomalies, highlighting new mechanisms in QCD hadronization.

Findings

Proton-to-pion ratio increases with centrality.

Charged particle cross section falls off more steeply at high centrality.

Same-side hadron production decreases with centrality.

Abstract

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-$p_T$ 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 $x_T=2p_T/ \sqrt s$ 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.