Two particles move along the edges of equilateral $△ABC$ in the direction $A\Rightarrow B\Rightarrow C\Rightarrow A$, starting simultaneously and moving at the same speed. One starts at $A$, and the other starts at $B$. The midpoint of the line segment joining the two particles traces out a path that encloses a region $R$. What is the ratio of the area of $R$ to the area of $△ABC$?