Mixing angle of doubly heavy baryons in QCD

We calculate the mixing angles between the spin-1/2, Xi(bc)-Xi'(bc) and Omega(bc)-Omega'(bc) states of doubly heavy baryons within the QCD sum rules method. It is found that the mixing angles are large and have the values phi(Xi bc) = 16 degrees +/- 5 degrees and phi(Omega bc) = 18 degrees +/- 6 degrees, respectively. The mixing angles are slightly smaller compared to the predictions of the non-relativistic quark model, phi(Xi bc) = 25.5 degrees and phi(Omega bc) = 25.9 degrees.