In-medium modification of $\rho$-mesons produced in heavy ion collisions

The mass shift $\Delta m_{\rho}$ and width broadening $\Delta\Gamma_{\rho}$ of $\rho$ mesons produced in heavy ion collisions is estimated using a general formula which relates the in-medium mass shift of a particle to the real part of the forward scattering amplitude ${\rm Re} f(E)$ of this particle on constituents of the medium and $\Delta\Gamma$ to the corresponding cross section. It is found that in high energy ($E/A \ga 100~$GeV) heavy ion collisions the $\rho$ width broadening is large and $\rho$ (or $\omega$) peak could hardly be observed in $e^+e^-(\mu^+\mu^-)$ effective mass distributions. In low energy collisions ($E/A \sim$ a few GeV) a broad (a few hundred MeV) enhancement is expected at the position of the $\rho$ peak.