  We have investigated the process of $\Lambda_b\to \Lambda D\bar{D}$, by
taking into account the contributions from the $s$-wave $D\bar{D}$ interaction
within the coupled-channel unitary approach, and the intermediate $\psi(3770)$
resonance. In addition to the peak of the $\psi(3770)$, an enhancement near the
$D\bar{D}$ mass threshold is found in the $D\bar{D}$ invariant mass
distributions, which should be the reflection of the $D\bar{D}$ bound state. We
would like to encourage our experimental colleagues to measure the $D\bar{D}$
invariant mass distribution of the $\Lambda_b\to \Lambda D\bar{D}$ process,
which is crucial to search for the $D\bar{D}$ bound state and to understand the
heavy-hadron heavy-hadron interactions.
