  We consider evolution equations describing the scale dependence of the wave
function of a baryon containing an infinitely heavy quark and a pair of light
quarks at small transverse separations, which is the QCD analogue of the helium
atom.The evolution equations depend on the relative helicity of the light
quarks. For the aligned helicities, we find that the equation is completely
integrable, that is it has a nontrivial integral of motion, and obtain exact
analytic expressions for the eigenfunctions and the anomalous dimensions. The
evolution equation for anti-aligned helicities contains an extra term that
breaks integrability and creates a "bound state" with the anomalous dimension
separated from the rest of the spectrum by a finite gap. The corresponding
eigenfunction is found using numerical methods. It describes the momentum
fraction distribution of the light quarks in, e.g., $\Lambda_b$-baryon at large
scales.
