Mass and $K\Lambda$ coupling of $N^{\ast }(1535)$

Abstract

Using resonance isobar model and effective Lagrangian approach, from recent BES results on $J/\psi \to \bar{p}p\eta$ and $\psi \to \bar{p}{K}^{+}\Lambda$, we deduce the ratio between effective coupling constants of $N^{\ast }(1535)$ to $K\Lambda$ and $p\eta$ to be $R\equiv g_{N^{\ast }(1535)K\Lambda }/g_{N^{\ast }(1535)p\eta }=1.3\pm 0.3$. With previous known value of $g_{N^{\ast }(1535)p\eta }$, the obtained new value of $g_{N^{\ast }(1535)K\Lambda }$ is shown to reproduce recent $pp\to p{K}^{+}\Lambda$ near-threshold cross section data as well. Taking into account this large $N^{\ast }K\Lambda$ coupling in the coupled channel Breit-Wigner formula for the $N^{\ast }(1535)$, 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 $K\Lambda$. The implication on the nature of $N^{\ast }(1535)$ is discussed.

9 pages, 4 figures