Results are presented of an analysis of proton and charged pion azimuthal distributions measured with respect to the reaction plane in Au ϩ Au collisions at a beam momentum of about 11A GeV/c. The azimuthal anisotropy is studied as a function of particle rapidity and transverse momentum for different centralities of the collisions. The triple differential ͑in rapidity, transverse momentum, and azimuthal angle͒ distributions are reconstructed. A comparison of the results with a previous analysis of charged-particle and transverse energy flow as well as with model predictions are presented. ͓S0556-2813͑97͒05711-7͔ PACS number͑s͒: 25.75.Dw

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 1

Experimental results and a detailed analysis are presented of the transverse energy and charged particle azimuthal distributions measured by the E877 * On leave from Moscow Engineering Physics Institute, Moscow, 115409, Russia 1 collaboration for different centralities of Au+Au collisions at a beam momentum of 10.8 A GeV/c. The anisotropy of these distributions is studied with respect to the reaction plane reconstructed on an event-by-event basis using the transverse energy distribution measured by calorimeters. Results are corrected for the reaction plane resolution. For semicentral events we observe directed flow signals of up to ten percent. We observe a stronger anisotropy for slow charged particles. For both the charged particle and transverse energy distributions we observe a small but non zero elliptic anisotropy with the major axis pointing into the reaction plane. Combining the information on transverse energy and charged particle flow we obtain information on the flow of nucleons and pions. The data are compared to event generators and the need to introduce a mean field or nucleon-nucleon potential is discussed.

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