The role of $N^*(1535)$ in $pp \to pp ϕ$ and $π^- p \to n ϕ$ reactions

Abstract

The near threshold $ϕ$ meson production in proton-proton and $π^- p$ collisions is studied with the assumption that the production mechanism is due to the sub-$Nϕ$-threshold $N^*(1535)$ resonance. The $π^0$, $η$ and $ρ^0$-meson exchanges for proton-proton collisions are considered. It is shown that the contribution to the $pp \to pp ϕ$ reaction from the t-channel $π^0$ meson exchange is dominant. With a significant $N^*(1535)Nϕ$ coupling ($g^2_{N^*(1535)N ϕ}/4 π$ = 0.13), both $pp \to pp ϕ$ and $π^- p \to n ϕ$ data are very well reproduced. The significant coupling of the $N^*(1535)$ resonance to $N ϕ$ is compatible with previous indications of a large $s \bar{s}$ component in the quark wave function of the $N^*(1535)$ resonance and may be the real origin of the significant enhancement of the $ϕ$ production over the naive OZI-rule predictions.