Azimuthal asymmetry of neutral pion emission in Au+Au reactions at 1 GeV/nucleon

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 ${\mathrm{\ensuremath{\pi}}}^{0}$'s perpendicular to the reaction plane is observed. The azimuthal asymmetry is dependent on the ${\mathrm{\ensuremath{\pi}}}^{0}$ momentum: the ${\mathrm{\ensuremath{\pi}}}^{0}$ 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 ${\mathrm{\ensuremath{\pi}}}^{0}$ than for charged particles and neutrons.