Pseudorapidity dependence of anisotropic flows in relativistic heavy-ion collisions

The pseudorapidity dependence of anisotropic flows $v_{1}$, $v_{2}$, $v_{3}$ , and $v_{4}$ of charged hadrons in heavy-ion collisions at the Relativistic Heavy Ion Collider is studied in a multi-phase transport model. We find that while the string melting scenario, in which hadrons that are expected to be formed from initial strings are converted to their valence quarks and antiquarks, can explain the measured $p_{T}$-dependence of $v_{2}$ and $ v_{4} $ of charged hadrons at midrapidity with a parton scattering cross section of about 10 \textrm{mb}, the scenario without string melting reproduces better the recent data on $v_{1}$ and $v_{2}$ of charged hadrons at large pseudorapidity in Au + Au collisions at $\sqrt{s}=200$ AGeV . Our results thus suggest that a partonic matter is formed during early stage of relativistic heavy ion collisions only around midrapidity and that strings remain dominant at large rapidities. The $p_{T}$-dependence of $v_{1} $, $v_{2}$, $v_{3}$ and $v_{4}$ for charged hadrons at forward pseudorapidity is also predicted, and we find that while $v_{1}$ and $v_{2}$ are appreciable at large pseudorapidity the higher-order anisotropic flows $v_{3}$ and $v_{4} $ are essentially zero.