Directed and Elliptic Flow in Pb+Pb collisions at 40 and 158 AGeV
  Directed and elliptic flow are reported for charged pions and protons as a function of transverse momentum, rapidity, and centrality in 40 and 158 AGeV Pb + Pb collisions. The standard method of correlating particles with an event plane is used. The directed flow of protons is small and shows little variation near to midrapidity, but rises fast towards projectile rapidity in the 40 AGeV data. For most peripheral collisions the flat region becomes negative resulting in $v_1$ changing sign three times. Elliptic flow doesn't seem to change very much from 40 AGeV to 158 AGeV. The difference is smaller than anticipated from the overall energy dependence from AGS to RHIC. 
Alexander Wetzler, N. Borghini, P.M. Dinh, J.-Y. Ollitrault, A.M.   Poskanzer, S.A. Voloshin and the NA49 Collaboration