In-medium properties of the phi meson with phi N resonant contributions

TL;DR

This paper investigates the in-medium properties of the phi meson in cold nuclear matter, highlighting the significant role of resonant phi N interactions and their impact on the meson's spectral function and mass shift.

Contribution

It introduces models including phi N resonant interactions to explain phi meson modifications in nuclear matter, extending beyond traditional K-bar K cloud effects.

Findings

Resonant phi N states contribute significantly to phi self-energy.

In-medium broadening of phi up to 50 MeV at normal density.

Possible mass shift of phi meson by up to 35 MeV at nuclear matter density.

Abstract

Nuclear production experiments report missing absorption processes of the in-medium phi meson. Contributions arising from the K-bar K cloud have already been widely studied, and therefore we investigate the phi-meson properties in cold nuclear matter with the additional inclusion of resonant phi N interactions. Two models are considered which dynamically generate N*-like states close to the phi N threshold. We find that these states, together with the non-resonant part of the amplitude, contribute to the phi self-energy with the same order of magnitude as the K-bar K effects. At non-vanishing nuclear density, both models lead to an additional in-medium broadening of the phi, up to around 50 MeV. Furthermore, at least one of the models is compatible with a mass shift to lower energies of up to 35 MeV at threshold and normal matter density. Finally, a double-peak structure appears in the spectral function due to the mixing of resonance-hole modes with the $\phi$ quasi-particle peak. These results converge into the direction of the experimental findings.