Measurement of the $W\to e\hat{I}½$ and $Z/γ^* \to e^+e^-$ Production Cross Sections at Mid-rapidity in Proton-Proton Collisions at $\sqrt{s}$ = 500 GeV

Abstract

We report measurements of the charge-separated $W^{+(-)}\to e^{+(-)}+\hat{I}{½}_e(\bar{\hat{I}}{½}_e)$ and $Z/γ^* \to e^+e^-$ production cross sections at mid-rapidity in proton-proton collisions at $\sqrt{s}$ = 500 GeV. These results are based on 13.2 pb${}^{-1}$ of data recorded in 2009 by the STAR detector at RHIC. Production cross sections for W bosons that decay via the $e\hat{I}½$ channel were measured to be $\ddot{I}ƒ(pp\to W^{+}X)\cdot BR(W^{+}\to e^{+}\hat{I}{½}_e)$ = 117.3 \pm 5.9(stat) \pm 6.2(syst) \pm 15.2(lumi) pb, and $\ddot{I}ƒ(pp\to W^{-}X)\cdot BR(W^{-}\to e^{-}\bar{\hat{I}}{½}_e)$ = 43.3 \pm 4.6(stat) \pm 3.4(syst) \pm 5.6(lumi) pb. For $Z/γ^*$ production, $σ(pp \to Z/γ^* X) \cdot BR(Z/γ^* \to e^+ e^-)$ = 7.7 \pm 2.1(stat) ${}_{-0.9}^{+0.5}$(syst) \pm 1.0(lumi) pb for di-lepton invariant masses $m_{e^{+}{e}^{-}}$ between 70 and 110 GeV/$c^2$. First measurements of the W cross section ratio, $\ddot{I}ƒ(pp\to W^{+}X)/\ddot{I}ƒ(pp\to W^{-}X)$, at $\sqrt{s}$ = 500 GeV are also reported. Theoretical predictions, calculated using recent parton distribution functions, are found to agree with the measured cross sections.

14 pages, 12 figures, submitted to Physical Review D