  The LHCb collaboration newly measured the decay rate of doubly charmed baryon
$\Xi^{++}_{cc}\to\Xi^{'+}\pi^+$ and a ratio of its branching fraction with
respect to that of the decay $\Xi^{++}_{cc}\to\Xi^{+}\pi^+$ is reported as
$1.41\pm 0.17\pm 0.10$. This result conflicts with the theoretical predictions
made by several groups. In our previous work, following the prescription given
in early literature where the $us$ diquark in $\Xi^{+}_{c}$ is assumed to be a
scalar whereas in $\Xi^{'+}_{c}$ is a vector i.e. the spin-flavor structure of
$\Xi^{+}_{c}$ is $[us]_0 c$ and that of $\Xi^{'+}_{c}$ is $[us]_1 c$, we
studied the case of $\Xi^{++}_{cc}\to\Xi^{(')+}$ with the light front quark
model. Numerically we obtained
$\Gamma(\Xi^{++}_{cc}\to\Xi^{'+}\pi^+)/\Gamma(\Xi^{++}_{cc}\to\Xi^{+}\pi^+)=0.56\pm0.18$
which is about half of the data. While abandoning the presupposition, we
suppose the spin-flavor structure of $us$ in $\Xi^{+}_{c}$ may be a mixture of
scalar and vector, namely the spin-flavor function of $\Xi^{+}_{c}$ could be
${\rm cos}\theta\, [us]_{0}[c]+{\rm sin}\theta\, [us]_{1}[c]$. An alternative
combination $-{\rm sin}\theta\,[us]_{0}[c]+{\rm cos}\theta\, [us]_{1}[c]$ would
correspond to $\Xi^{'+}_{c}$. Introducing the mixing mechanism the ratio
$\Gamma(\Xi^{++}_{cc}\to\Xi^{'+}\pi^+)/\Gamma(\Xi^{++}_{cc}\to\Xi^{+}\pi^+)$
depends on the mixing angle $\theta$. With the mixing scenario, the theoretical
prediction on the ratio between the transition rate of
$\Xi^{+}_{cc}\to\Xi^{'+}_c$ and that of $\Xi^{+}_{cc}\to\Xi^{+}_c$ can coincide
with the data as long as $\theta=16.27^\circ\pm2.30^\circ$ or
$85.54^\circ\pm2.30^\circ$ is set. Definitely, more precise measurements on
other decay portals of $\Xi^{+}_{cc}$ are badly needed for testing the mixing
mechanism and further determining the mixing angle.
