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Apparent and Actual Shifts in Mass and Width of Phi Mesons Produced in Heavy-Ion Collisions

We present a method of analyzing invariant-mass spectra of kaon pairs resulting from decay of $ϕ$ mesons produced in high-energy heavy-ion collisions. It can be used to extract the shifts in the mass and the width ($ΔM$ and $ΔΓ$) of the $ϕ$ mesons when they are inside the dense matter formed in these collisions. We illustrate our method with the help of available preliminary data. Extracted values of $ΔM$ and $ΔΓ$ are significantly larger than those obtained with an earlier method. Our results are consistent with the experimentally observed $p_T$ dependence of the mass shift. Finally, we present a phenomenological relation between $ΔM$ and $ΔΓ$. It provides a useful constraint on theories which predict the values of these two quantities.