Colour coherence in small collision systems

TL;DR

This paper investigates how colour coherence influences jet quenching and azimuthal anisotropy in small collision systems, using Monte Carlo simulations and hydrodynamic models to compare different collision scenarios.

Contribution

It demonstrates that colour coherence affects nuclear modification factors but has limited impact on azimuthal anisotropy in small collision systems.

Findings

Colour coherence increases $R_{AA}$ but minimally affects $v_2$.

Nuclear modification factors are similar in O+O and Pb+Pb collisions at the same multiplicity.

Hydrodynamic profiles show shape differences do not alter $R_{AA}$ significantly.

Abstract

The observation of collectivity in collisions of small systems has constituted a challenge for the heavy-ion community for over a decade now. The absence of jet quenching in those systems presents an apparent contradiction to the presence of an azimuthal anisotropy of high-$p_\perp$ particles. In the present work, we investigate the role of colour coherence in this puzzle. For that, we use the \textsc{Jewel} Monte Carlo model in its latest version, which includes effects of colour coherence in the jet-medium interactions. We then compare the two scenarios, with and without colour coherence, and quantify the effect on hadron and jet $R_{AA}$ as well as on high-$p_\perp$ $v_2$. The results indicate that, although coherence effects do account for an increase in $R_{AA}$, they do not affect $v_2$ to the same extent. Using hydrodynamic profiles generated with \textit{Trajectum} we compare O+O and Pb+Pb collisions at the same charged particle multiplicity and find that the nuclear modification factors are the same in both systems despite their different shapes.