Di-electron spectrum at mid-rapidity in $p+p$ collisions at $\sqrt{s}=200$ GeV

Abstract

We report on mid-rapidity mass spectrum of di-electrons and cross sections of pseudoscalar and vector mesons via $e^{+}{e}^{-}$ decays, from $\sqrt{s}=200$ GeV $p+p$ collisions, measured by the large acceptance experiment STAR at RHIC. 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 $\ddot{I}‰\to e^{+}{e}^{-}$ invariant yields are consistent with previous measurements. The mid-rapidity yields ($dN/dy$) of $\ddot{I}•$ and $J/\ddot{I}ˆ$ are extracted through their di-electron decay channels and are consistent with the previous measurements of $\ddot{I}•\to K^{+}{K}^{-}$ and $J/\ddot{I}ˆ\to e^{+}{e}^{-}$. Our results suggest a new upper limit of the branching ratio of the $\hat{I}\cdot \to e^{+}{e}^{-}$ of $1.7\times 10^{-5}$ at 90% confidence level.

15 pages, 17 figures, 4 tables. Published