Abstract

We report systematic measurements of dielectron (e+e−) invariant-mass Mee spectra at midrapidity in Au + Au collisions at √s NN = 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 (0.40 < M ee < 0.75 MeV/c2 ) compared to hadronic cocktail simulations at freeze-out. Models that include an in-medium broadening of the ρ-meson spectral function consistently describe the observed excess. In addition, we report acceptance-corrected dielectron-excess spectra for Au + Au collisions at midrapidity (|yee| < 1) in the 0–80% centrality bin for each collision energy. The integrated excess yields for 0.4 < Mee < 0.75 GeV/c2 , normalized by the charged particle multiplicity at midrapidity, are compared with previously published measurements for Au + Au at √s NN = 19.6 and 200 GeV. Models that include an in-medium broadening of the ρ-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.

Document Type

Article

Publication Date

2023

Notes/Citation Information

© 2023 American Physical Society

Digital Object Identifier (DOI)

https://doi.org/10.1103/PhysRevC.107.L061901

Funding Information

We thank S. Endres, O. Linnyk, E. L. Bratkovskaya, and R. Rapp for discussions and model calculations. We thank the RHIC Operations Group and RCF at BNL, the NERSC Center at LBNL, and the Open Science Grid consortium for providing resources and support. This work was supported in part by the Office of Nuclear Physics within the U.S. DOE Office of Science, the U.S. National Science Foundation, the National Natural Science Foundation of China, the Chinese Academy of Science, the Ministry of Science and Technology of China and the Chinese Ministry of Education, the Higher Education Sprout Project by Ministry of Education at NCKU, the National Research Foundation of Korea, the Czech Science Foundation and Ministry of Education, Youth and Sports of the Czech Republic, the Hungarian National Research, Development and Innovation Office, the New National Excellency Programme of the Hungarian Ministry of Human Capacities, the Department of Atomic Energy and Department of Science and Technology of the Government of India, the National Science Centre and WUT ID-UB of Poland, the Ministry of Science, Education and Sports of the Republic of Croatia, the German Bundesministerium für Bildung, Wissenschaft, Forschung and Technologie (BMBF), the Helmholtz Association, the Ministry of Education, Culture, Sports, Science, and Technology (MEXT), and the Japan Society for the Promotion of Science (JSPS).

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