Cross Section and Parity Violating Spin Asymmetries of $W^\pm$ Boson Production in Polarized $p+p$ Collisions at $\sqrt{s}=500$ GeV

The PHENIX collaboration
Adare, A. , Afanasiev, S. , Aidala, C. , Ajitanand, N.N. , Akiba, Y. , Akiimoto, R. , Alexander, J. , Al-Taani, H. , Andrews, K.R. , Angerami, A.
Phys.Rev.Lett. 106 (2011) 062001, 2011.

Abstract (data abstract)
Large parity violating longitudinal single-spin asymmetries $A^{e^+}_L$ = $-0.86^{+0.30}_{-0.14}$ and $A^{e^-}_L$ = $0.88^{+0.12}_{-0.71}$ are observed for inclusive high transverse momentum electrons and positrons in polarized $p + p$ collisions at a center of mass energy of $\sqrt{s}$ = 500 GeV with the PHENIX detector at RHIC. These $e^{\pm}$ come mainly from the decay of $W^{\pm}$ and $Z^0$ bosons, and their asymmetries directly demonstrate parity violation in the couplings of the $W^{\pm}$ to the light quarks. The observed electron and positron yields were used to estimate $W^{\pm}$ boson production cross sections for the $e^{\pm}$ channels of $\sigma$ $(pp \rightarrow W^+ X) \times BR(W^+ \rightarrow e^+\nu_e) = 144.1 \pm 21.2$(stat)$^{+3.4}_{-10.3}$(syst)$\pm 15\%(norm)$ pb, and $\sigma (pp \rightarrow W^- X) \times BR(W^- \rightarrow e^- \bar{\nu}_e)$ = 31.7 $\pm$12.1(stat)$^{+10.1}_{-8.2}$(syst) $\pm$ 15%(norm) pb.

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