Colour coherence in small collision systems

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.