Measurement of the Effective Weak Mixing Angle in $p\overline{p}\to Z/{\gamma }^{*}\to {\ell }^{+}{\ell }^{-}$ Events

We present a measurement of the effective weak mixing angle parameter ${\sin }^2{\theta }_{\text{eff}}^{\ell }$ in $p\overline{p}\to Z/{\gamma }^{*}\to {\mu }^{+}{\mu }^{-}$ events at a center-of-mass energy of 1.96 TeV, collected by the D0 detector at the Fermilab Tevatron Collider and corresponding to $8.6{\mathrm{fb}}^{-1}$ of integrated luminosity. The measured value of ${\sin }^2{\theta }_{\text{eff}}^{\ell }[\mu \mu ]=0.23016\pm 0.00064$ is further combined with the result from the D0 measurement in $p\overline{p}\to Z/{\gamma }^{*}\to e^{+}{e}^{-}$ events, resulting in ${\sin }^2{\theta }_{\text{eff}}^{\ell }[\text{comb}]=0.23095\pm 0.00040$. This combined result is the most precise measurement from a single experiment at a hadron collider and is the most precise determination using the coupling of the $Z/{\gamma }^{*}$ to light quarks.

Figure 1

Comparison between the $A_{FB}$ distributions in the background-subtracted data and the MC with different ${\sin }^2{\theta }_W^p$ values in the pythia generator. The ${\chi }^2$ corresponds to the MC with the best-fit value of ${\sin }^2{\theta }_W^p$. The uncertainties are statistical only.

Figure 2

Comparison of ${\sin }^2{\theta }_{\text{eff}}^{\ell }(M_Z)$ measured by D0 with results from other experiments. The average of measurements from the LEP and SLD Collaborations [1] is also shown.