In-medium effects in $ϕ$ meson production in heavy-ion collisions from subthreshold to relativistic energies

We investigate the hidden strange $ϕ$ meson production in heavy-ion collisions from subthreshold ($E_{kin}\approx 1$ A GeV) to relativistic ($E_{kin}\approx 21$ A TeV) energies as well as its coupling to the open strange mesons (kaons, antikaons) and their productions. Our study is based on the off-shell microscopic Parton-Hadron-String Dynamics (PHSD) transport approach which is applicable for the dynamical description of strongly interacting hadronic and partonic degrees-of-freedom created in heavy-ion collisions. Implementing novel meson-baryon and meson-hyperon production channels for $ϕ$ mesons, calculated within a T-matrix coupled channel approach based on the extended SU(6) chiral effective Lagrangian model, along with the collisional broadening of the $ϕ$-meson in-medium spectral function, we find a substantial enhancement of $ϕ$ meson production in heavy-ion collisions, especially at sub- and near-thresholds. This allows to describe the experimentally observed strong enhancement of the $ϕ/K^-$ ratio at low energies without including hypothetical decays of heavy baryonic resonances to $ϕ$ as in alternative approaches. Moreover, we show that in spite of a stronger contribution from enhanced $ϕ$ to $K^-$ production, the majority of the experimental data for different A+A systems at low energies favor the scenario with in-medium modifications of the kaon and antikaon properties in the hot and dense environment. Moreover, we study the influence of the final state interactions of $K, \bar K$ mesons on the reconstruction of $ϕ$'s by the by invariant mass method.

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