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$phi$ meson self-energy in nuclear matter from $phi N$ resonant interactions

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 Added by Daniel Cabrera
 Publication date 2016
  fields
and research's language is English




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The $phi$-meson properties in cold nuclear matter are investigated by implementing resonant $phi N$ interactions as described in effective approaches including the unitarization of scattering amplitudes. Several $N^*$-like states are dynamically generated in these models around $2$ GeV, in the vicinity of the $phi N$ threshold. We find that both these states and the non-resonant part of the amplitude contribute sizably to the $phi$ collisional self-energy at finite nuclear density. These contributions are of a similar strength as the widely studied medium effects from the $bar K K$ cloud. Depending on model details (position of the resonances and strength of the coupling to $phi N$) we report a $phi$ broadening up to about $40$-$50$ MeV, to be added to the $phitobar K K$ in-medium decay width, and an attractive optical potential at threshold up to about $35$ MeV at normal matter density. The $phi$ spectral function develops a double peak structure as a consequence of the mixing of resonance-hole modes with the $phi$ quasi-particle peak. The former results point in the direction of making up for missing absorption as reported in $phi$ nuclear production experiments.



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We investigate the $phi$ meson nuclear transparency using some recent theoretical developments on the $phi$ in medium self-energy. The inclusion of direct resonant $phi N$-scattering and the kaon decay mechanisms leads to a $phi$ width much larger than in most previous theoretical approaches. The model has been confronted with photoproduction data from CLAS and LEPS and the recent proton induced $phi$ production from COSY finding an overall good agreement. The results support the need of a quite large direct $phi N$-scattering contribution to the self-energy.
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.
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