Hydrodynamic modeling of pseudorapidity flow correlations in relativistic heavy-ion collisions and the torque effect

TL;DR

This paper investigates the torque effect in relativistic heavy-ion collisions, showing that initial fluctuations and emission asymmetries cause decorrelation of event-plane angles across pseudorapidity, with larger effects at RHIC than LHC.

Contribution

It provides a detailed hydrodynamic analysis of the torque effect, comparing model predictions with experimental data and highlighting the role of initial state fluctuations.

Findings

Significant torque effect observed in simulations.

Magnitude of decorrelation larger at RHIC than LHC.

Model results consistent with CMS experimental data.

Abstract

We analyze correlations between the event-plane angles in different intervals of pseudorapidity within the 3+1-dimensional viscous hydrodynamics with the Glauber-model initial conditions. As predicted earlier, the fluctuations in the particle production mechanism in the earliest stage, together with asymmetry of the emission profiles in pseudorapidity from the forward- and backward going wounded nucleons, lead to the torque effect, namely, decorrelation of the event-plane angles in distant pseudorapidity bins. We use two- or three-bin measures of correlation functions to quantify the effect, with the latter compared to the recent data from the CMS collaboration. We find a sizable torque effect, with magnitude larger at RHIC than at the LHC.