Modification of the φ-meson spectrum in nuclear matter

The vacuum spectrum of the φ-meson is characterized by its decay into KK̄. Modifications of the KK̄-loops in baryonic matter change this spectrum. We calculate these in-medium modifications taking both s- and p-wave kaon-nucleon interactions into account. We use results of the in-medium K and K̄ spectra determined previously from a coupled channel approach based on a chiral effective Lagrangian. Altogether we find a very small shift of the φ meson mass, by less than 10 MeV at normal nuclear matter density ρ₀. The in-medium decay width of the φ meson increases such that its life time at ρ = ρ₀ is reduced to less than 5 fm/c. It should therefore be possible to observe medium effects in reactions such as π^- p → φn in heavy nuclei, where the φ meson can be produced with small momentum.