The mass shift Δmρ and width broadening ΔΓρ of ρ 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 Ref(E) of this particle on constituents of the medium and ΔΓ to the corresponding cross section. It is found that in high energy (E/A ≳ 100 GeV) heavy ion collisions the ρ width broadening is large and ρ (or ω) peak could hardly be observed in e+e-(μ+μ-) effective mass distributions. In low energy collisions (E/A ∼ a few GeV) a broad (a few hundred MeV) enhancement is expected at the position of the ρ peak.
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(The first numbers in Eqs. (28) and (29) refer to pN scattering, the second ones to pi). The conclusion is that at low energy heavy ion collisions p-peak may be observed in e+e-or p+p-effective mass distribution as a broad enhancement approximately at the position of p-mass. We are indebted to K. Boreskov, A. Kaidalov, G. Brown and A. Sibirtsev for illuminating discussions. B.I. thanks A. Smirnitsky and V. Smolyankin for the help in getting information about experimental data. This work was supported in part by JNTAS G rant 93-0283, CRDF grant RP2-132, Schweizerischer National Fonds grant 7SUPJO48716 and by the RFBR grant 97-02-16131. V. L. E. acknowledges support of BMBF, Bonn, Germany.