Measurement of $\sin^2\theta^{\rm lept}_{\rm eff}$ using $e^+e^-$ pairs from $\gamma^*/Z$ bosons produced in $p\bar{p}$ collisions at a center-of-momentum energy of 1.96 TeV

TL;DR

This paper reports a precise measurement of the effective electroweak mixing parameter $ ext{sin}^2 heta^{ ext{lept}}_{ ext{eff}}$ using electron-positron pairs from $ ext{p}ar{ ext{p}}$ collisions at 1.96 TeV, confirming Standard Model predictions.

Contribution

First measurement of $ ext{sin}^2 heta^{ ext{lept}}_{ ext{eff}}$ using $e^+e^-$ pairs at Tevatron, combining with muon data for improved precision.

Findings

$ ext{sin}^2 heta^{ ext{lept}}_{ ext{eff}} = 0.23248 \u00b1 0.00053$

Combined $ ext{sin}^2 heta^{ ext{lept}}_{ ext{eff}} = 0.23221 \u00b1 0.00046$

Derived $ ext{sin}^2 heta_W = 0.22400 \u00b1 0.00045$ and $W$ mass of $80.328 \u00b1 0.024$ GeV/$c^2$

Abstract

At the Fermilab Tevatron proton-antiproton ($p\bar{p}$) collider, Drell-Yan lepton pairs are produced in the process $p \bar{p} \rightarrow e^+e^- + X$ through an intermediate $\gamma^*/Z$ boson. The forward-backward asymmetry in the polar-angle distribution of the $e^-$ as a function of the $e^+e^-$-pair mass is used to obtain $\sin^2\theta^{\rm lept}_{\rm eff}$, the effective leptonic determination of the electroweak-mixing parameter $\sin^2\theta_W$. The measurement sample, recorded by the Collider Detector at Fermilab (CDF), corresponds to 9.4~fb$^{-1}$ of integrated luminosity from $p\bar{p}$ collisions at a center-of-momentum energy of 1.96 TeV, and is the full CDF Run II data set. The value of $\sin^2\theta^{\rm lept}_{\rm eff}$ is found to be $0.23248 \pm 0.00053$. The combination with the previous CDF measurement based on $\mu^+\mu^-$ pairs yields $\sin^2\theta^{\rm lept}_{\rm eff} = 0.23221 \pm 0.00046$. This result, when interpreted within the specified context of the standard model assuming $\sin^2 \theta_W = 1 - M_W^2/M_Z^2$ and that the $W$- and $Z$-boson masses are on-shell, yields $\sin^2\theta_W = 0.22400 \pm 0.00045$, or equivalently a $W$-boson mass of $80.328 \pm 0.024 \;{\rm GeV}/c^2$.