Subthreshold phi meson production in heavy ion collisions

Within a transport code of BUU type the production of Φ mesons in the reactions Ni+Ni at 1.93 A GeV and Ru + Ru at 1.69 A GeV is studied.
New elementary reaction channels ρN(Δ) → ΦN and πN(1520)→ ρN are included.
In spite of a substantial increase of the Φ multiplicities by these channels the results stay below the tentative numbers extracted from experimental data.