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Abstract

Transverse momentum spectra and rapidity densities, $dN/dy$, of protons, antiprotons, and net protons ($p\ensuremath{-}\overline{p}$) from central (0%--5%) $\mathrm{A}\mathrm{u}+\mathrm{A}\mathrm{u}$ collisions at $\sqrt{{s}_{NN}}=200\text{ }\text{ }\mathrm{G}\mathrm{e}\mathrm{V}$ were measured with the BRAHMS experiment within the rapidity range $0\ensuremath{\le}y\ensuremath{\le}3$. The proton and antiproton $dN/dy$ decrease from midrapidity to $y=3$. The net-proton yield is roughly constant for $y&lt;1$ at $dN/dy\ensuremath{\sim}7$, and increases to $dN/dy\ensuremath{\sim}12$ at $y\ensuremath{\sim}3$. The data show that collisions at this energy exhibit a high degree of transparency and that the linear scaling of rapidity loss with rapidity observed at lower energies is broken. The energy loss per participant nucleon is estimated to be $73\ifmmode\pm\else\textpm\fi{}6\text{ }\text{ }\mathrm{G}\mathrm{e}\mathrm{V}$.