\title{Measurements of longitudinal flow decorrelation in Au+Au

Collisions at $\sqrt{s_{NN}}$ = 200 GeV from the STAR Collaboration}

flow event plane

can improve our understanding of the longitudinal fluctuation of the QGP at

the initial state, and provide important

constraints for  (3+1)D hydrodynamical models.

Recent calculations\cite{Pang:2015zrq} indicate a stronger longitudinal decorrelation at RHIC

energies than at the LHC. In this presentation, we will report the decorrelation

measurements in Au+Au collisions at 200 GeV from STAR collaboration. By

using

the Forward Meson Spectrometer (FMS, $2.5 < |\eta| <4.5 $) and Time Projection

Chamber (TPC, $|\eta |<1.0 $) detectors,

the flow decorrelation can be measured in a rapidity gap around 2, and

the non-flow effect is significantly suppressed.

The results will be presented for different harmonic orders and centralities. The comparison

with the measurement from Pb+Pb at 2.76 TeV and calculations from

different models will also be discussed.