Source velocity at relativistic beams of 4He

The source velocities (β = ν/c) extracted from rapidity plots of the fragment invariant probability distribution in terms of the longitudinal versus transversal velocity components has been studied for 4He + Au collisions at 4 and 14.6 GeV. It was found transition from broad range source velocities distribution in case of 4He(4 GeV) + Au to fixed source velocity in case of 4He(14.6 GeV) + Au.