Drastic Enhancement of Composite Fermion Mass near Landau Level Fillingν=12

We have determined the effective mass of composite fermions in the vicinity of half Landau level filling and observe a mass enhancement by as much as 40% as the filling factor $\nu$ approaches $\nu =\frac{1}{2}$. These measurements provide the first experimental data for the energetics of this novel fermion system as $\nu \to \frac{1}{2}$. The apparently divergent particle mass indicates that the system at exactly $\nu =\frac{1}{2}$ is not an ordinary Fermi liquid.