 Solution

For a rate measurement of the small mixing angle ${\theta }_{13}$, choose the first fast disappearance maximum,A 47 km baseline instead lies near the slow oscillation maximum associated with ${\theta }_{12}$. Its much lower flux, approximately falling as $1/L^2$, and the many fast oscillations washed out by a reactor's broad energy spectrum make it a poor choice for this simple ${\theta }_{13}$ design. A medium-baseline spectral experiment can still constrain neutrino oscillation parameters if it has enough events and resolution; 47 km is not intrinsically useless, but it is not the optimal short-baseline rate experiment. In a, ${\theta }_{13}$ also affects the slow envelope through ${\cos }^4{\theta }_{13}$, so the sensitivity there is not identically zero.