Abstract
We report systematic measurements of dielectron () invariant-mass spectra at midrapidity in collisions at = 27, 39, and 62.4 GeV taken with the STAR detector at the Relativistic Heavy Ion Collider. For all energies studied, a significant excess yield of dielectrons is observed in the low-mass region () compared to hadronic cocktail simulations at freeze-out. Models that include an in-medium broadening of the -meson spectral function consistently describe the observed excess. In addition, we report acceptance-corrected dielectron-excess spectra for collisions at midrapidity ( 1) in the 0–80% centrality bin for each collision energy. The integrated excess yields for , normalized by the charged particle multiplicity at midrapidity, are compared with previously published measurements for at = 19.6 and 200 GeV. Models that include an in-medium broadening of the -meson spectral function consistently describe the observed excess. The normalized excess yields in the low-mass region show no significant collision energy dependence. The data, however, are consistent with model calculations that demonstrate a modest energy dependence.
- Received 27 February 2023
- Accepted 4 May 2023
DOI:https://doi.org/10.1103/PhysRevC.107.L061901
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