  Rapidity decorrelation in high energy heavy-ion collisions is one of the hot
topics in understanding longitudinal dynamics of the quark gluon plasma (QGP).
In this study we employ an integrated dynamical model with full three
dimensional relativistic hydrodynamics and perform event-by-event numerical
simulations of Pb+Pb collisions at the LHC energy. We analyze factorization
ratios to understand rapidity decorrelation from hydrodynamic fluctuations and
initial longitudinal fluctuations. We show that factorization breaking happens
due to both hydrodynamic fluctuations and initial longitudinal fluctuations. We
conclude hydrodynamic fluctuations and initial longitudinal fluctuations are
both important in understanding rapidity decorrelation.
