QCD sum rule analysis of spin-orbit splitting in baryons

• Published in: Annals of physics 1990-03, Vol.198 (2), p.203-251
• Main Author: Leinweber, Derek B
• Format: Article
• Language: English
• ISSN: 0003-4916; 1096-035X
• DOI: 10.1016/0003-4916(90)90251-I

A determination of spin-orbit splitting in N and Λ using the QCD sum rule technique of Shifman, Vainshtein, and Zakharov is presented. The QCD sum rules coupling to J P = 1 2 − nucleons, first considered by Belyaev and Ioffe are shown to provide a consistent description of N 1 2 − (1535) . The QCD sum rules coupling to the low-lying Δ 1 2 + , Λ 1 2 − , and Λ 3 2 − , are presented as these sum rules have not been previously considered in the literature. The non-perturbative calculations of spin-orbit splitting and odd parity excitation energies in the low-lying states of N and Λ are in agreement with experimental data. This is in contrast to conventional quark models. The large spin-orbit splitting in Λ resonances arises without invoking coupling to the KN scattering channel. The reduction of the strange quark condensate relative to the u or d quark condensate acts to increase the spin-orbit splitting in the low-lying Λ resonances. The results do not exclude coupling of Λ(1405) to the KN channel provided any additional spin-orbit splitting arising from the coupling is of the order of 30 MeV. Finally the Δ 1 2 + sum rules cast doubt on the existence of the unconfirmed (one ∗) Δ 1 2 + (1550) resonance.