We present experimental data on directed flow in semicentral Au+Au collisio
ns at incident energies from 90 to 400 A MeV. For the first time for this e
nergy domain, the data are presented in a transverse momentum differential
way. We study the first order Fourier coefficient upsilon (1) for different
particle species and establish a gradual change of its patterns as functio
n of incident energy and for different regions in rapidity.