Longitudinal decorrelation measures of flow magnitude and event-plane angles in ultra-relativistic nuclear collisions

TL;DR

This paper investigates the forward-backward correlations of harmonic flow in ultra-relativistic Pb+Pb collisions at the LHC, introducing new measures and comparing hydrodynamic model predictions with experimental data.

Contribution

It introduces new decorrelation measures for flow and analyzes their hierarchy and factorization properties using hydrodynamic simulations.

Findings

Hierarchy observed between flow decorrelation measures

Confirmation of factorization relations

Qualitative agreement with ATLAS and CMS data

Abstract

We discuss the forward-backward correlations of harmonic flow in Pb+Pb collisions at the CERN Large Hadron Collider (LHC), applying standard multibin measures, as well as proposed here new measures. We illustrate the methods with hydrodynamic model simulations based on event-by-event initial conditions from the wounded quark model with asymmetric rapidity emission profiles. Within the model we examine independently the event-plane angle and the flow magnitude decorrelations. We find specific hierarchy between various flow decorrelation measures and confirm certain factorization relations. We find qualitative agreement of the model and the data from the ATLAS and CMS Collaborations.