  The mass spectra of singly charmed and bottom baryons,
$\Lambda_{c/b}(1/2^\pm,3/2^-)$ and $\Xi_{c/b}(1/2^\pm,3/2^-)$, are investigated
using a nonrelativistic potential model with a heavy quark and a light diquark.
The masses of the scalar and pseudoscalar diquarks are taken from a chiral
effective theory. The effect of $U_A(1)$ anomaly induces an inverse hierarchy
between the masses of strange and non-strange pseudoscalar diquarks, which
leads to a similar inverse mass ordering in $\rho$-mode excitations of singly
heavy baryons.
