Disappearance of Back-To-Back High-$p_T$ Hadron Correlations in Central $\mathrm{A}\mathrm{u}+\mathrm{A}\mathrm{u}$ Collisions at $\sqrt{s_{NN}}=200\mathrm{G}\mathrm{e}\mathrm{V}$

Azimuthal correlations for large transverse momentum charged hadrons have been measured over a wide pseudorapidity range and full azimuth in $\mathrm{A}\mathrm{u}+\mathrm{A}\mathrm{u}$ and $p+p$ collisions at $\sqrt{s_{NN}}=200\mathrm{G}\mathrm{e}\mathrm{V}$. The small-angle correlations observed in $p+p$ collisions and at all centralities of $\mathrm{A}\mathrm{u}+\mathrm{A}\mathrm{u}$ collisions are characteristic of hard-scattering processes previously observed in high-energy collisions. A strong back-to-back correlation exists for $p+p$ and peripheral $\mathrm{A}\mathrm{u}+\mathrm{A}\mathrm{u}$. In contrast, the back-to-back correlations are reduced considerably in the most central $\mathrm{A}\mathrm{u}+\mathrm{A}\mathrm{u}$ collisions, indicating substantial interaction as the hard-scattered partons or their fragmentation products traverse the medium.