Excited Baryon Spectroscopy in the 1/N_c Expansion

摘要

We analyze the masses of the negative parity SU(6) 70-plet baryons using the 1/N_c expansion to order 1/N_c and to first order in SU(3) breaking. At this level of precision there are twenty predictions which include the well known Gell-Mann Okubo and equal spacing relations together with four new relations involving SU(3) breaking splittings in different SU(3) multiplets. Although the breaking of SU(6) symmetry occurs at zeroth order in 1/N_c, it turns out to be small. The dominant source of the breaking is the hyperfine interaction which is of order 1/N_c. The spin-orbit interaction, of zeroth order in 1/N_c, is entirely fixed by the splitting between the singlet states Λ(1405) and Λ(1520), and the spin-orbit puzzle is solved by the presence of other zeroth order operators involving flavor exchange.