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We report systematic measurements of dielectron ($e^{\pm}e^{\pm}$)invariant-mass $M_{ee}$ spectra at mid-rapidity in Au+Au collisions at$\sqrt{s_{NN}}$ = 27, 39, and 62.4 GeV taken with the STAR detector at theRelativistic Heavy Ion Collider. For all energies studied, a significant excessyield of dielectrons is observed in the low-mass region (0.40$ < M_{ee} < 0.75$MeV/$c^2$) compared to hadronic cocktail simulations at freeze-out. Models thatinclude an in-medium broadening of the $\rho$-meson spectral functionconsistently describe the observed excess. In addition, we reportacceptance-corrected dielectron-excess spectra for Au+Au collisions atmid-rapidity ($\left|y_{ee}\right|$ $<$ 1) in the 0$-$80% centrality bin foreach collision energy. The integrated excess yields for $0.4 < M_{ee} < 0.75\\textrm{GeV}/c^{2}$, normalized by the charged particle multiplicity atmid-rapidity, are compared with previously published measurements for Au+Au at$\sqrt{s_{NN}}$ = 19.6 and 200 GeV. The normalized excess yields in thelow-mass region show no significant collision energy dependence. The data,however, are consistent with model calculations that demonstrate a modestenergy dependence.

Measurements of Dielectron Production in Au$+$Au Collisions at $\sqrt{s_{NN}}$= 27, 39, and 62.4 GeV from the STAR Experiment