1/N_c corrections to the SU(4)_c symmetry for L = 1 baryons: The three towers

In the large N_c limit, the mass spectrum of the L=1 orbitally excited baryons A* has a very simple structure, with states degenerate in pairs of spins J=(1/2,3/2),(3/2,5/2), corresponding to irreducible representations (towers) of the contracted SU(4)_c symmetry group. The mixing angles are completely determined in this limit. Using a mass operator approach, we study 1/N_c corrections to this picture, pointing out a fourfold ambiguity in the correspondence of the observed baryons with the large N_c states. For each of the four possible assignments, we fit the coefficients of the quark operators contributing to the mass spectrum to O(N_c^-1). We comment on the implications of our results for the constituent quark model description of these states.