$\bf p$-$\bf p$ minimum-bias dijets and nonjet quadrupole in relation to conjectured collectivity (flows) in high-energy nuclear collisions

TL;DR

This paper challenges the interpretation of ridge-like correlations in small and large collision systems as evidence of collective flow, presenting data that support a non-hydrodynamic, two-component model of hadron production.

Contribution

It provides spectrum, correlation, and fluctuation data supporting a two-component model and shows that the nonjet quadrupole is a distinct phenomenon, questioning the flow interpretation.

Findings

Correlation structures in small systems can be explained without hydrodynamic flow.

Nonjet quadrupole component scales with multiplicity similarly in small and large systems.

Data are consistent with a two-component (soft+dijet) model rather than a collective medium.

Abstract

Recent observations of ridge-like structure in $p$-$p$ and $p$-$A$ angular correlations at the RHIC and LHC have been interpreted to imply collective motion in smaller collision systems. It is argued that if correlation structures accepted as manifestations of flow in $A$-$A$ collisions appear in smaller systems collectivity (flow) must extend to the smaller systems. But the argument could be reversed to conclude that such structures appearing in $A$-$A$ collisions may not imply hydrodynamic flow. I present spectrum, correlation and fluctuation data from RHIC $p$-$p$ and Au-Au collisions and $p$-$p$, $p$-Pb and Pb-Pb results from the LHC described accurately by a two-component (soft+dijet) model of hadron production. I also present evidence for a significant $p$-$p$ nonjet (NJ) quadrupole ($v_2$) component with $n_{ch}$ systematics directly related to $A$-$A$ NJ quadrupole systematics. The combination suggests that soft, dijet and NJ quadrupole components are distinct phenomena in all cases, inconsistent with hadron production from a common bulk medium exhibiting collective motion (flow).