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

We present a measurement of the fundamental parameter of the standard model, the weak mixing angle ${\sin }^2{\theta }_{\text{eff}}^{\ell }$ which determines the relative strength of weak and electromagnetic interactions, in $p\overline{p}\to Z/{\gamma }^{*}\to e^{+}{e}^{-}$ events at a center of mass energy of 1.96 TeV, using data corresponding to $9.7{\mathrm{fb}}^{-1}$ 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 ${\sin }^2{\theta }_{\text{eff}}^{\ell }=0.23147\pm 0.00047$ is the most precise measurement from light quark interactions to date, with a precision close to the best LEP and SLD results.

Figure 1

Comparison between the $A_{FB}$ distributions measured in the background-subtracted data and the MC simulations for the three kinematic regions, with the corresponding ${\chi }^2$ per degree of freedom. ${\sin }^2{\theta }_W$ in the MC simulations is 0.231 39. The error bars are statistical only.

Figure 2

Comparison of measured ${\sin }^2{\theta }_{\text{eff}}^{\ell }$ with results from other experiments. The average is a combination of $A_{FB}^{0,\ell }$, $A_l(P_{\tau })$, $A_{lr}(\mathrm{SLD})$, $A_{FB}^{0,b}$, $A_{FB}^{0,c}$, and $Q_{FB}^{\mathrm{had}}$ measurements from the LEP and SLD collaborations [1].