Mass and $KΛ$ coupling of $N^*(1535)$

Abstract

Using resonance isobar model and effective Lagrangian approach, from recent BES results on $J/ψ\to\bar ppη$ and $ψ\to\bar pK^+Λ$, we deduce the ratio between effective coupling constants of $N^*(1535)$ to $KΛ$ and $pη$ to be $R\equiv g_{N^*(1535)KΛ}/g_{N^*(1535)pη} =1.3\pm 0.3$. With previous known value of $g_{N^*(1535)pη}$, the obtained new value of $g_{N^*(1535)KΛ}$ is shown to reproduce recent $pp\to pK^+Λ$ near-threshold cross section data as well. Taking into account this large $N^*KΛ$ coupling in the coupled channel Breit-Wigner formula for the $N^*(1535)$, its Berit-Wigner mass is found to be around 1400 MeV, much smaller than previous value of about 1535 MeV obtained without including its coupling to $KΛ$. The implication on the nature of $N^*(1535)$ is discussed.