  The quark flavor sector of the Standard Model is a fertile ground to look for
new physics effects through a unitarity test of the Cabbibo-Kobayashi-Maskawa
(CKM) matrix. We present a lattice QCD calculation of the scalar and the vector
form factors (over a large $q^2$ region including $q^2 = 0$) associated with
the $D \rightarrow Kl{\nu}$ semi-leptonic decay. This calculation will then
allow us to determine the central CKM matrix element, $V_{cs}$ in the Standard
Model, by comparing the lattice QCD results for the form factors and the
experimental decay rate. This form factor calculation has been performed on the
$N_f =2+1+1$ MILC HISQ ensembles with the physical light quark masses.
