Systematic study of high $p_{\rm T}$ hadron production in small collision systems by the PHENIX experiment at RHIC

Abstract

High $p_{\rm T}$ hadrons in the small systems of $d/^3$He+Au and $p$+Al/Au collisions have been measured at the midrapidity ($|\eta|<0.35$) as well as at the forward and backward rapidities ($1.2<|\eta|<2.4$) at $\sqrt{s_{NN}}$=200GeV. A clear system and centrality ordering in the $R_{p/d/{\rm HeA}}$ was observed for midrapidity $\pi^0$ production. Hadron $R_{\rm cp}$ as a function of rapidity in forward and backward regions show an opposite trend to what HIJING++ predicted. Together with the difference of $R_{\rm cp}$ in $p$+Al/Au collisions, the observation can be understood consistently with the measured long-range two-particle correlations, hinting the possible medium creation similar to A+A collisions.