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

TL;DR

This paper investigates the role of the $N^*(1535)$ resonance in near-threshold $ o$ phi meson production in proton-proton and pion-proton collisions, highlighting the dominance of $ ho^0$ exchange and a strong $N^*(1535)N o ext{phi}$ coupling.

Contribution

It demonstrates that the $N^*(1535)$ resonance significantly contributes to $ ext{phi}$ production, with a large $N^*(1535)N o ext{phi}$ coupling consistent with its large $sar{s}$ component.

Findings

The $ ho^0$ meson exchange dominates the $pp o pp ext{phi}$ reaction.

A strong $N^*(1535)N o ext{phi}$ coupling reproduces experimental data.

The $N^*(1535)$ resonance's large $sar{s}$ component explains the enhanced $ ext{phi}$ production.

Abstract

The near threshold $\phi$ meson production in proton-proton and $\pi^- p$ collisions is studied with the assumption that the production mechanism is due to the sub-$N\phi$-threshold $N^*(1535)$ resonance. The $\pi^0$, $\eta$ and $\rho^0$-meson exchanges for proton-proton collisions are considered. It is shown that the contribution to the $pp \to pp \phi$ reaction from the t-channel $\pi^0$ meson exchange is dominant. With a significant $N^*(1535)N\phi$ coupling ($g^2_{N^*(1535)N \phi}/4 \pi$ = 0.13), both $pp \to pp \phi$ and $\pi^- p \to n \phi$ data are very well reproduced. The significant coupling of the $N^*(1535)$ resonance to $N \phi$ 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 $\phi$ production over the naive OZI-rule predictions.