Jet Quenching in the Smallest Hadronic Collision Systems

TL;DR

This paper provides pQCD predictions for high-momentum particle suppression in very light ion collisions, revealing non-trivial suppression patterns and identifying systems suitable for observing QGP formation in small systems.

Contribution

It introduces new predictions for particle suppression in small ion collisions and highlights specific light systems as promising for studying QGP effects.

Findings

Suppression scales approximately as (AB)^{1/3} in symmetric and asymmetric systems.

${}^{3} ext{He}$ and ${}^{6} ext{Li}$ are ideal for observing partonic energy loss.

Energy loss models predict near-zero $v_2$ in small systems, inconsistent with experimental $v_2 > 0$.

Abstract

We present perturbative quantum chromodynamics (pQCD) predictions for high-momentum particle yield modification in very light ion collisions - ${}^{10}\mathrm{B}+{}^{10}\mathrm{B}$, ${}^{6}\mathrm{Li}+{}^{6}\mathrm{Li}$, ${}^{4}\mathrm{He}+{}^{4}\mathrm{He}$, and ${}^{3}\mathrm{He}+{}^{3}\mathrm{He}$ - with and without medium-induced energy loss. We find non-trivial suppression in symmetric systems from ${}^{208}\mathrm{Pb}+{}^{208}\mathrm{Pb}$ to ${}^{3}\mathrm{He}+{}^{3}\mathrm{He}$ and in asymmetric $A+B$ systems, with the suppression scaling approximately as $R_{AB} \simeq (\sqrt{AB})^{1/3}$. Further, we find that ${}^{3}\mathrm{He}$ and ${}^{6}\mathrm{Li}$ offer particularly clean environments for observing final-state partonic energy loss from quark-gluon plasma (QGP) formation in extremely small systems. Finally, we show that energy loss models generically predict $v_2\{\mathrm{SP}\} \approx 0$ in small systems, indicating that the large measured $v_2 > 0$ in $p+{}^{208}\mathrm{Pb}$ is not due to energy loss.