A pentaquark model of the negative parity Lambda(1405)

Abstract

We test a pentaquark model of the negative parity hyperon Lambda(1405). We use the model where valence four quarks and one antiquark move in a potential relativisticaly and interact with themselves and each other through gluon and NG boson. We calculate mass shift of the system and find that there are two Lambda(1405) with almost degenerate mass: one flavor singlet and one flavor octet. We calclate also sigma-term and scalar form factor of the hyperon and show their usefulness to deduce the number of valence quark in the hypeon.