Effects of saturation and fluctuating hotspots for flow observables in ultrarelativistic heavy-ion collisions

TL;DR

This paper explores how saturation dynamics and fluctuating hotspots influence flow observables in ultrarelativistic heavy-ion collisions, showing improved agreement with experimental data through the MC-EKRT model enhancements.

Contribution

It introduces fluctuating hotspots into the MC-EKRT event generator, revealing their impact on flow coefficients and multiplicity distributions, and improves the modeling of collision-energy dependence.

Findings

Hotspots enhance saturation effects and improve data agreement.

The ratio of flow coefficients $v_3$ to $v_2$ is sensitive to saturation dynamics.

Fluctuations in saturation scale are essential for reproducing multiplicity tails.

Abstract

We investigate the effects of saturation dynamics on midrapidity flow observables by adding fluctuating hotspots into the novel Monte Carlo EKRT (MC-EKRT) event generator for high-energy nuclear collisions. We demonstrate that the intensity of the saturation effects significantly affects the ratio between the flow coefficients $v_3$ and $v_2$ at the LHC. Adding a hotspot substructure to the nucleons enhances the saturation effects and improves the agreement with the measured data. We show that the collision-energy dependence of the flow coefficients obtained using the MC-EKRT initial states with hotspots is improved in comparison with the earlier event-by-event EKRT model. In addition, we present the results for the charged hadron multiplicity distribution in Pb+Pb collisions at the LHC, and show that the minijet-multiplicity originating fluctuations of the saturation scale included in MC-EKRT, as well as the presence of hotspots, are necessary for describing the measured large-multiplicity tail in the distribution.