Medium Modifcations of Mesons in Elementary Reactions and Heavy-Ion Collisions

Experimental searches for modifications of vector mesons in the nuclear medium are reviewed. Data on $\rho,\omega$ and $\Phi$ mesons are presented. The results have been obtained in elementary reactions with proton and photon beams as well as in heavy-ion collisions. Compared to the free particle properties, the $\omega$ and $\Phi$ meson are found to drop in mass at normal nuclear matter density by 9-14% and 3.5% whereas their widths are reported to increase by factors of about 16 and 3.6, respectively. For the $\rho$ meson, conflicting results on in-medium mass shifts and broadening have been published. The experimental data are compared to recent model calculations.