Investigation of $D^+\to\tau^+\nu$

Using data taken with the CLEO-c detector at the $\psi(3770)$ resonance, we compare our recent measurement of ${\cal{B}}(D^+\to\mu^+\nu)$ with ${\cal{B}}(D^+\to\tau^+\nu)$. The ratio of branching ratios should be 2.65 in the Standard Model with any deviation indicating a breakdown of lepton universality.