Measurement of the electric charge of the top quark in $t\overline{t}$ events

We present a measurement of the electric charge of top quarks using $t\overline{t}$ events produced in $p\overline{p}$ collisions at the Tevatron. The analysis is based on fully reconstructed $t\overline{t}$ pairs in $\text{lepton}+\text{jets}$ final states. Using data corresponding to $5.3{\mathrm{fb}}^{-1}$ of integrated luminosity, we exclude the hypothesis that the top quark has a charge of $Q=-4/3e$ at a significance greater than 5 standard deviations. We also place an upper limit of 0.46 on the fraction of such quarks that can be present in an admixture with the standard model top quarks ($Q=+2/3e$) at a 95% confidence level.

Figure 1

Distributions of charge templates for $b$ and $\overline{b}$ jets extracted from dijet events following the application of kinematic corrections described in the text.

Figure 2

Combined distribution in the charge $Q_t$ for $t\overline{t}$ candidates in data compared with expectations from the SM and the BSM. The background contribution (BG) is represented by the green-shaded histogram. The expected distributions are normalized to unity and used as the PDF ${\mathcal{P}}^{\mathrm{SM}}(Q_t)$ and ${\mathcal{P}}^{\mathrm{BSM}}(Q_t)$ in Eq. (3).

Figure 3

Distributions of $\ln (\mathrm{\Lambda })$ for the SM (histograms on the right) and BSM (histograms on the left) models from $10^9\mathrm{PE}$, compared to the measurement (arrow). The solid lines show the expected distributions, while the dashed histograms show the distributions expected in the absence of systematic uncertainties. The value of $\ln ({\mathrm{\Lambda }}_{\mathrm{D}})$ is displayed by the black vertical line.

Figure 4

Confidence belts from the Feldman-Cousins approach for 1 SD (inner), 3 SD (middle), and 5 SD (outer). The red solid line shows the average of the measured values $f_{\text{meas}}$ for each input fraction $f_{\text{true}}$ and the vertical dashed line represents the fraction ($f=0.88$) observed in the data.