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

TL;DR

This study measures high transverse momentum hadron production in small collision systems at RHIC, revealing system and centrality dependencies and unexpected rapidity trends that suggest possible medium formation similar to larger nucleus collisions.

Contribution

It provides the first detailed measurements of high pT hadrons in small systems at RHIC across different rapidities and centralities, challenging existing models and indicating potential medium effects.

Findings

Clear system and centrality dependence in $R_{p/d/{ m HeA}}$ at midrapidity

Opposite rapidity trend in $R_{cp}$ compared to HIJING++ predictions

Evidence of medium-like effects in small systems from long-range correlations

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.