We show that semileptonic and electromagnetic decays involving spin-1/2 doubly heavy bc baryons are very sensitive to hyperfine mixing in their wave functions. We further show how heavy quark spin symmetry relations, obtained in the infinite heavy quark mass limit and near zero recoil, could be used to extract the admixtures in a model independent way from semileptonic decay data. On the other hand the infinite heavy quark mass limit gives wrong predictions in the electromagnetic case.
$\Omega_c$ excited states with heavy-quark spin symmetry
