  We propose the transverse velocity ($\beta_T$) dependence of the
anti-deuteron to deuteron ratio as a new observable to search for the QCD
critical point in heavy-ion collisions. The QCD critical point can attract the
system evolution trajectory in the QCD phase diagram, which is known as
focusing effect. To quantify this effect, we employ thermal model and hadronic
transport model to simulate the dynamical particle emission along a
hypothetical focusing trajectory near critical point. We found the focusing
effect can lead to anomalous $\beta_T$ dependence of $\bar{p}/p$, $\bar{d}/d$
and $^3\overline{\text{He}}/^3\text{He}$ ratios. We examined the $\beta_T$
dependence of $\bar{p}/p$ and $\bar{d}/d$ ratios of central Au+Au collisions at
$\sqrt{s_{NN}}$ = 7.7 to 200 GeV measured by the STAR experiment at RHIC.
Surprisingly, we only observe a negative slope in $\beta_T$ dependence of
$\bar{d}/d$ ratio at $\sqrt{s_{NN}}$ = 19.6 GeV, which indicates the trajectory
evolution has passed through the critical region. In the future, we could
constrain the location of the critical point and/or width of the critical
region by making precise measurements on the $\beta_T$ dependence of
$\bar{d}/d$ ratio at different energies and rapidity.
