Observation of anisotropic event shapes and transverse flow in ultrarelativistic Au+Au collisions.

Abstract

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 beyond that expected due to fluctuations in particle multiplicity. The signal decreases for peripheral and very central collisions. The amplitude of the flow signal reaches up to 7% of the mean E_T.