Jet Quenching in the Smallest Hadronic Collision Systems

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.

Contribution to the 2026 QCD session of the 60th Rencontres de Moriond