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Register a new userCollision Broadening of the Phi Meson in Baryon Rich Hadronic Matter
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Phi meson-baryon cross sections, estimated within a one-boson-exchange model, serve as input for a calculation of the collision rates in hot hadronic matter. We find that the width of the phi meson is modified through collisions with baryons by 1-10 MeV at 160 MeV temperature depending on the baryon fugacity. Thermalization of the phi in high energy heavy ion collisions is discussed.
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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.
We study the formation of baryons as composed of quarks and diquarks in hot and dense hadronic matter in a Nambu--Jona-Lasinio (NJL)--type model. We first solve the Dyson-Schwinger equation for the diquark propagator and then use this to solve the Dyson-Schwinger equation for the baryon propagator. We find that stable baryon resonances exist only in the phase of broken chiral symmetry. In the chirally symmetric phase, we do not find a pole in the baryon propagator. In the color-superconducting phase, there is a pole, but is has a large decay width. The diquark does not need to be stable in order to form a stable baryon, a feature typical for so-called Borromean states. Varying the strength of the diquark coupling constant, we also find similarities to the properties of an Efimov states.
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.
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.
We consider a chiral baryon-meson model for nucleons and their parity partners in mirror assignment interacting with pions, sigma and omega mesons to describe the liquid-gas transition of nuclear matter together with chiral symmetry restoration in the high density phase. Within the mean-field approximation the model is known to provide a phenomenologically successful description of the nuclear-matter transition. Here, we go beyond this approximation and include mesonic fluctuations by means of the functional renormalization group. While these fluctuations do not lead to major qualitative changes in the phase diagram of the model, beyond mean-field, one is no-longer free to adjust the parameters so as to reproduce the binding energy per nucleon, the nuclear saturation density, and the nucleon sigma term all at the same time. However, the prediction of a clear first-order chiral transition at low temperatures inside the high baryon-density phase appears to be robust.
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