Further study on 5q configuration states in the chiral SU(3) quark model

The structure of the 5q configuration states with strangeness S=+1 is further studied in the chiral SU(3) quark model based on our previous work. We calculate the energies of fifteen low configurations of the 5q system, four lowest configurations of Jπ=12− with 4q partition [4]orb(0s4)[31]σf, four of Jπ=12+ with 4q partition [31]orb(0s30p)[4]σf and seven of Jπ=12+ with 4q partition [4]orb(0s30p)[31]σf. Some modifications are made in this further study, i.e., the orbital wave function is extended as an expansion of 4 different size harmonic oscillator forms; three various forms (quadratic, linear and error function form) of the color confinement potential are considered; the states with 4q partition [4]orb(0s30p)[31]σf are added, which are unnegligible in the Jπ=12+ case and were not considered in our previous paper, further the mixing between configurations [31]orb(0s30p)[4]σf and [4]orb(0s30p)[31]σf is also investigated. The results show that the T=0 state is still always the lowest one for both Jπ=12− and Jπ=12+ states, and Jπ=12−, T=0 state is always lower than that of Jπ=12+. All of these modifications can only offer several tens to hundred MeV effect, and the theoretical value of the lowest state is still about 245 MeV higher than the experimental mass of Θ+. It seems to be difficult to get the calculated mass close to the observed one with the reasonable parameters in the framework of the chiral SU(3) quark model when the model space is chosen as a 5q cluster.