Eur. Phys. J. A (2016) 52: 97
https://doi.org/10.1140/epja/i2016-16097-x

Regular Article - Theoretical Physics

Decorrelation of anisotropic flow along the longitudinal direction

¹ Frankfurt Institute for Advanced Studies, Ruth-Moufang-Strasse 1, 60438, Frankfurt am Main, Germany
² Institute for Theoretical Physics, Goethe University, Max-von-Laue-Strasse 1, 60438, Frankfurt am Main, Germany
³ GSI Helmholtzzentrum für Schwerionenforschung, Planckstr. 1, 64291, Darmstadt, Germany
⁴ Key Laboratory of Quark & Lepton Physics (MOE) and Institute of Particle Physics, Central China Normal University, 430079, Wuhan, China
⁵ Nuclear Science Division MS70R0319, Lawrence Berkeley National Laboratory, 94720, Berkeley, CA, USA

^* e-mail: pang@fias.uni-frankfurt.de

Received: 20 November 2015
Accepted: 7 February 2016
Published online: 20 April 2016

Abstract

The initial energy density distribution and fluctuations in the transverse direction lead to anisotropic flow of final hadrons through collective expansion in high-energy heavy-ion collisions. Fluctuations along the longitudinal direction, on the other hand, can result in decorrelation of anisotropic flow in different regions of pseudorapidity ( . Decorrelation of the 2nd- and 3rd-order anisotropic flow with different gaps for final charged hadrons in high-energy heavy-ion collisions is studied in an event-by-event (3+1)D ideal hydrodynamic model with fully fluctuating initial conditions from A Multi-Phase Transport (AMPT) model. The decorrelation of anisotropic flow of final hadrons with large gaps is found to originate from the spatial decorrelation along the longitudinal direction in the AMPT initial conditions through hydrodynamic evolution. The decorrelation is found to consist of both a linear twist and random fluctuation of the event plane angles. The agreement between our results and recent CMS data in most centralities suggests that the string-like mechanism of initial parton production in AMPT model captures the initial longitudinal fluctuation that is responsible for the measured decorrelation of anisotropic flow in Pb+Pb collisions at LHC. Our predictions for Au+Au collisions at the highest RHIC energy show stronger longitudinal decorrelation, indicating larger longitudinal fluctuations at lower beam energies. Our study also calls into question some of the current experimental methods for measuring anisotropic flow and the quantitative extraction of transport coefficients through comparisons to hydrodynamic simulations that do not include longitudinal fluctuations.