  The incident energy at which the azimuthal distributions in semi-central
heavy ion collisions change from in-plane to out-of-plane enhancement, E_tran,
is studied as a function of mass of emitted particles, their transverse
momentum and centrality for Au+Au collisions. The analysis is performed in a
reference frame rotated with the sidewards flow angle, Theta_flow, relative to
the beam axis. A systematic decrease of E_tran as function of mass of the
reaction products, their transverse momentum and collision centrality is
evidenced. The predictions of a microscopic transport model (IQMD) are compared
with the experimental results.
