Puzzles at High $p_T$ at RHIC and Their Resolution

Abstract

Several puzzles about the data at high $p_T$ in heavy-ion collisions are listed. The resolution of them all is given in the framework of parton recombination. More specifically, it is the recombination of the soft and semi-hard shower partons that enhances the region $3<p_T<9$ GeV/c, and gives rise to the large $p/\pi$ ratio in AuAu collisions. The Cronin effect can be explained in terms of final-state interaction for both $\pi$ and $p$. The structure of jets produced in AuAu is different from that in $pp$ collisions. The suppression of $R_{CP}$ in forward production can also be understood by extending the same hadronization scheme at $\eta=0$ to $\eta>0$ without the introduction of any new physics.