Measurement of the effective weak mixing angle in $p\bar{p}\rightarrow Z/γ^{*}\rightarrow e^{+}e^{-}$ events

TL;DR

The paper reports a precision measurement of the effective weak mixing angle $\sin^2\theta_W^{\text{eff}}_{\ell}$ in $p\bar{p}$ collisions at $\sqrt{s}=1.96$ TeV using $Z/\gamma^{*} \rightarrow e^+e^-$ events collected with the D0 detector, corresponding to $9.7\,\text{fb}^{-1}$ of data. The analysis exploits the forward-backward asymmetry $A_{FB}$ as a function of the dilepton invariant mass $M_{ee}$ around the $Z$ pole, with three event categories (CC-CC, CC-EC, EC-EC) and expanded electron acceptance; a new electron energy calibration reduces the dominant systematic from the energy scale. Detector modeling, data-driven background estimates, and MC corrections including NNLO QCD and PDF reweighting are combined to construct $A_{FB}$ templates for different input values of $\sin^2\theta_W^{\text{eff}}_{\ell}$ and extract the measurement via template fits. The result, $\sin^2\theta_W^{\text{eff}}_{\ell} = 0.23147 \pm 0.00047$, is the most precise determination from light-quark interactions to date and is consistent with the world average and LEP/SLD measurements.

Abstract

We present a measurement of the fundamental parameter of the standard model, the weak mixing angle, in $p\bar{p}\rightarrow Z/γ^{*}\rightarrow e^{+}e^{-}$ events at a center of mass energy of 1.96 TeV, using data corresponding to 9.7 fb$^{-1}$ of integrated luminosity collected by the D0 detector at the Fermilab Tevatron. The effective weak mixing angle is extracted from the forward-backward charge asymmetry as a function of the invariant mass around the Z boson pole. The measured value of $\sin^2θ_{\text{eff}}^{\text{$\ell$}}=0.23147 \pm 0.00047$ is the most precise measurement from light quark interactions to date, with a precision close to the best LEP and SLD results.

Figures (2)

• Figure 1: (color online). Comparison between the $A_{FB}$ distributions measured in the background-subtracted data and the MC for the three kinematic regions, with the corresponding $\chi^2$ per degree of freedom. $\sin^2 \theta_{W}$ in the MC is 0.23139. The error bars are statistical only.
• Figure 2: (color online). Comparison of measured $\sin^2\theta_{\text{eff}}^{\text{$\ell$}}$ with results from other experiments. The average is a combination of $A_{FB}^{0,\ell}$, $A_{l}(P_{\tau})$, $A_{lr}(\text{SLD})$, $A_{FB}^{0,b}$, $A_{FB}^{0,c}$, and $Q_{FB}^{\text{had}}$ measurements from the LEP and SLD Collaborations LEP-SLD.