The azimuthal angle distributions of neutral pions at midrapidity from Au+Au reactions at 1 GeV/nucleon incident energy have been measured. An enhanced emission of ${\mathrm{\pi }}^0$’s perpendicular to the reaction plane is observed. The azimuthal asymmetry is dependent on the ${\mathrm{\pi }}^0$ momentum: the ${\mathrm{\pi }}^0$ spectrum perpendicular to the reaction plane is harder than in the reaction plane. The strength of the observed asymmetry appears to be more pronounced for ${\mathrm{\pi }}^0$ than for charged particles and neutrons.

• Received 29 April 1993

DOI:https://doi.org/10.1103/PhysRevLett.71.835