QGP droplet formation in small asymmetric collision systems

TL;DR

This paper discusses evidence and implications of quark-gluon plasma formation in small asymmetric collision systems, challenging previous assumptions that QGP only forms in large collision systems, based on recent experimental and theoretical analyses.

Contribution

It provides a comprehensive review of experimental data and theoretical models supporting QGP formation in small systems, questioning traditional views on the conditions needed for QGP creation.

Findings

Evidence of collective behavior in small collision systems

QGP formation indicated in p-A and d-A collisions

Challenges to existing QGP formation theories

Abstract

The journal Nature recently published a letter titled "Creating small circular, elliptical, and triangular droplets of quark-gluon plasma" [1]. The basis for that claim is a combination of measured Fourier amplitudes $v_2$ and $v_3$ from collision systems $p$-Au, $d$-Au and $h$-Au (helion $h$ is the nucleus of atom $^3$He), Glauber Monte Carlo estimates of initial-state transverse collision geometries for those systems and hydro Monte Carlo descriptions of the $v_n$ data. Correspondence between hydro $v_n$ trends and data trends is interpreted as confirmation of "collectivity" occurring in the small collision systems, further interpreted to indicate QGP formation. QGP formation in small systems runs counter to pre-RHIC theoretical assumptions that QGP formation should require large collision systems (e.g. central A-A collisions). There is currently available a broad context of experimental data from $p$-$p$, A-A and $p$-Pb collisions at the RHIC and LHC against which the validity of the Nature letter claims may be evaluated. This talk provides a summary of such results and their implications. [1] Nature Phys. 15, no. 3, 214 (2019).}