Measurements of dielectron production in Au + Au collisions at sNN=200 GeV from the STAR experiment

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We report on measurements of dielectron $({e}^{+}{e}^{\ensuremath{-}})$ production in $\mathrm{Au}+\mathrm{Au}$ collisions at a center-of-mass energy of 200 GeV per nucleon-nucleon pair using the STAR detector at BNL Relativistic Heavy Ion Collider. Systematic measurements of the dielectron yield as a function of transverse momentum $({p}_{\mathrm{T}})$ and collision centrality show an enhancement compared to a cocktail simulation of hadronic sources in the low invariant-mass region $({M}_{ee}<1\phantom{\rule{4pt}{0ex}}\text{GeV}/{c}^{2})$. This enhancement cannot be reproduced by the $\ensuremath{\rho}$-meson vacuum spectral function. In minimum-bias collisions, in the invariant-mass range of $0.30--0.76\phantom{\rule{4.pt}{0ex}}\mathrm{GeV}/{c}^{2}$, integrated over the full ${p}_{\mathrm{T}}$ acceptance, the enhancement factor is $1.76\ifmmode\pm\else\textpm\fi{}0.06\phantom{\rule{0.28em}{0ex}}(\mathrm{stat}.)\ifmmode\pm\else\textpm\fi{}0.26\phantom{\rule{0.28em}{0ex}}(\mathrm{sys}.)\ifmmode\pm\else\textpm\fi{}0.29\phantom{\rule{0.28em}{0ex}}(\mathrm{cocktail})$. The enhancement factor exhibits weak centrality and ${p}_{\mathrm{T}}$ dependence in STAR's accessible kinematic regions, while the excess yield in this invariant-mass region as a function of the number of participating nucleons follows a power-law shape with a power of $1.44\ifmmode\pm\else\textpm\fi{}0.10$. Models that assume an in-medium broadening of the $\ensuremath{\rho}$-meson spectral function consistently describe the observed excess in these measurements. Additionally, we report on measurements of $\ensuremath{\omega}$- and $\ensuremath{\phi}$-meson production through their ${e}^{+}{e}^{\ensuremath{-}}$ decay channel. These measurements show good agreement with Tsallis blast-wave model predictions, as well as, in the case of the $\ensuremath{\phi}$ meson, results through its ${K}^{+}{K}^{\ensuremath{-}}$ decay channel. In the intermediate invariant-mass region $(1.1<{M}_{ee}<3\phantom{\rule{4pt}{0ex}}\text{GeV}/{c}^{2})$, we investigate the spectral shapes from different collision centralities. Physics implications for possible in-medium modification of charmed hadron production and other physics sources are discussed.

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