In-Plane Elliptic Flow of Resonance Particles in Relativistic Heavy-Ion Collisions

We analyze the second Fourier coefficient v₂ of the pion azimuthal distribution in noncentral heavy-ion collisions in a relativistic hydrodynamic model. The exact treatment of the decay kinematics of resonances leads to almost vanishing azimuthal anisotropy of pions near the midrapidity, while the matter elliptic flow is in plane at freeze-out. In addition, we reproduce the rapidity dependence of v₂ for pions measured in noncentral Pb+Pb collisions at 158AGeV. This suggests that resonance particles as well as stable particles constitute the in-plane flow and are important ingredients for the understanding of the observed pion flow.