Azimuthal correlations of pions in relativistic heavy-ion collisions at 1 GeV/nucleon

Triple differential cross sections of pions in heavy ion collisions at 1 GeV/nucleon are studied with the isospin quantum molecular dynamics (IQMD) model. After discussing general properties of Δ resonance and pion production we focus on azimuthal correlations: At projectile- and target-rapidities we observe an anticorrelation in the in-plane transverse momentum between pions and protons. At c.m.-rapidity, however, we find that high ${\mathit{p}}_{\mathit{t}}$ pions are being preferentially emitted perpendicular to the event plane. We investigate the causes of those correlations and their sensitivity on the density and momentum dependence of the real and imaginary part of the nucleon and pion optical potential.