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 $\phi$ mesons produced in high-energy heavy-ion collisions. It can be used to extract the shifts in the mass and the width ($\Delta M$ and $\Delta \Gamma$) of the $\phi$ 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 $\Delta M$ and $\Delta \Gamma$ 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 $\Delta M$ and $\Delta \Gamma$. It provides a useful constraint on theories which predict the values of these two quantities.