Di-electron spectrum at mid-rapidity in p + p collisions at √ s = 200 GeV
We report on the mid-rapidity mass spectrum of di-electrons and cross sections of pseudoscalar and vector mesons via e + e − decays, from √ s = 200 GeV p + p collisions, measured by the large-acceptance experiment STAR at the Relativistic Heavy Ion Collider. The ratio of the di-electron continuum to the combinatorial background is larger than 10% over the entire mass range. Simulations of di-electrons from light-meson decays and heavy-flavor decays (charmonium and open charm correlation) are found to describe the data. The extracted ω → e + e − invariant yields are consistent with previous measurements. The mid-rapidity yields (dN/dy) of φ and J/ψ are extracted through their di-electron decay channels and are consistent with the previous measurements of φ → K + K − and J/ψ → e + e −. Our results suggest a new upper limit of the branching ratio of the η → e + e − of 1.7 × 10−5 at the 90% confidence level.