In-Plane Elliptic Flow of Resonance Particles in Relativistic Heavy-Ion   Collisions
  We analyze the second Fourier coefficient $v_2$ of the pion azimuthal distribution in non-central 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 $v_2$ for pions measured in non-central Pb + Pb collisions at 158$A$ GeV. 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. 
Tetsufumi Hirano (Waseda Univ.)