Baryon Rapidity Loss in Relativistic $Au+Au$ Collisions

An excitation function of proton rapidity distributions for different centralities is reported from AGS Experiment E917 for $\mathrm{Au}+\mathrm{Au}$ collisions at 6, 8, and 10.8 GeV/nucleon. The rapidity distributions from peripheral collisions have a valley at midrapidity which smoothly change to distributions that display a broad peak at midrapidity for central collisions. The mean rapidity loss increases with increasing beam energy, whereas the fraction of protons consistent with isotropic emission from a stationary source at midrapidity decreases with increasing beam energy. The data suggest that the stopping is substantially less than complete at these energies.