Observation of Anisotropic Event Shapes and Transverse Flow in Ultrarelativistic Au + Au Collisions

Event shapes for Au + Au collisions at 11.4 GeV/c per nucleon were studied over nearly the full solid angle with the E877 apparatus. The analysis was performed by Fourier expansion of azimuthal distributions of the transverse energy (${E}_{T}$) measured in different pseudorapidity intervals. For semicentral collisions a pronounced event anisotropy is identified with a clear forward-backward anticorrelation. In the forward pseudorapidity interval up to 9% of the ${E}_{T}$ is in a directed component. The signal decreases for peripheral and very central collisions.