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"Excited Baryon Spectroscopy in the 1/Nc Expansion"
N.N. Scoccola
Proc. of the "II International Workshop on Hadron Physics: Effective Theories of Low Energy QCD", Coimbra, Portugal, September 25-29, 2002. Ed. A.H. Blin, B. Hiller, A.A. Osipov, M.C. Ruivo and E. van Beveren
AIP Conf. Proc., Vol.660 (2003) 48-61
We analyze the masses of the negative parity SU(6) 70-plet baryons using the 1/Nc expansion to order 1/Nc 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/Nc, it turns out to be small. The dominant source of the breaking is the hyperfine interaction which is of order 1/Nc. The spin-orbit interaction, of zeroth order in 1/Nc, 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.
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