  We calculate the threshold $T$ matrices of the light pseudoscalar meson and
heavy meson scattering to fourth order in heavy meson chiral perturbation
theory. We determine the low-energy constants by fitting to the lattice QCD
data points through both the perturbative and iterated methods and obtain the
physical scattering lengths in both formalisms. The values of the scattering
lengths tend to be convergent at fourth order for most of the channels in the
perturbative method. The value of the scattering length for the channel $DK
(I=0)$, which involves the bound state $D_{s0}^{*}(2317)$, is obtained
correctly in the iterated method. Based on the heavy diquark-antiquark
symmetry, we also estimate the meson and doubly charmed (bottom) baryon
scattering lengths, and find that the bound states can be generated with high
probability in the channels $\bar{K}\Xi_{cc}(I=0)$ and $\bar{K}\Xi_{bb}(I=0)$.
We strongly urge the LHCb Collaboration to look for the very narrow
$\bar{K}\Xi_{cc}$ state with $IJ^P=0{1\over 2}^-$ through either the
electromagnetic decay or the iso-spin violating strong decay $\Omega_{cc} \pi$.
