Abstract
The mass spectrum of the positive parity [56,2+] baryons is studied in the 1/Nc expansion up to and including O(1/Nc) effects with SU(3) symmetry breaking implemented to first order. A total of eighteen mass relations result, several of which are tested with the available data. The breaking of spin-flavor symmetry is dominated by the hyperfine interactions, while spin–orbit effects are found to be small.
Highlights
The mass spectrum of the positive parity [56, 2+] baryons is studied in the 1/Nc expansion up to and including O(1/Nc) effects with SU (3) symmetry breaking implemented to first order
In this letter the available empirical information is used to implement an analysis of the masses based on the 1/Nc expansion of QCD [2, 3], an approach that has turned out to be very successful in baryon phenomenology
The 1/Nc expansion has been applied to the ground state baryons [4, 5, 6, 7, 8, 9, 10], and to excited baryons, where the masses and decays of the negative parity spin-flavor 70plet [11, 12, 13, 14, 15] and the positive parity Roper 56-plet [16] have been analyzed
Summary
The mass spectrum of the positive parity [56, 2+] baryons is studied in the 1/Nc expansion up to and including O(1/Nc) effects with SU (3) symmetry breaking implemented to first order. In the mass range from 1600 to 2100 MeV there exists a set of positive parity baryons which might be assigned to an irreducible representation [56, 2+] of SU(6) ⊗ O(3), where SU(6) is the spin-flavor group and O(3) classifies the orbital excitations. This can be shown using reductions, valid for the symmetric representation, of matrix elements involving excited quark and/or core operators, such as: Sym | si | Sym
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