Dielectron Mass Spectra from Au+Au Collisions at $\sqrt{s_{\mathrm{NN}}}$ = 200 GeV

Abstract

We report the STAR measurements of dielectron ($e^{+}{e}^{-}$) production at midrapidity ($|y_{ee}|<$1) in Au+Au collisions at $\sqrt{s_{\mathrm{NN}}}$ = 200\,GeV. The measurements are evaluated in different invariant mass regions with a focus on 0.30-0.76 ($\rho$-like), 0.76-0.80 ($\omega$-like), and 0.98-1.05 ($\varphi$-like) GeV/$c^2$. The spectrum in the $\omega$-like and $\varphi$-like regions can be well described by the hadronic cocktail simulation. In the $\rho$-like region, however, the vacuum $\rho$ spectral function cannot describe the shape of the dielectron excess. In this range, an enhancement of 1.77$\pm$0.11(stat.)$\pm$0.24(sys.)$\pm$0.33(cocktail) is determined with respect to the hadronic cocktail simulation that excludes the $\rho$ meson. The excess yield in the $\rho$-like region increases with the number of collision participants faster than the $\omega$ and $\varphi$ yields. Theoretical models with broadened $\rho$ contributions through interactions with constituents in the hot QCD medium provide a consistent description of the dilepton mass spectra for the measurement presented here and the earlier data at the Super Proton Synchrotron energies.

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