Measurement of the top quark pair production cross section in the $\mathrm{\text{lepton}}+\mathrm{\text{jets}}$ channel in proton-antiproton collisions at $\sqrt{s}=1.96\mathrm{TeV}$

We present a measurement of the inclusive top quark pair production cross section in $p\overline{p}$ collisions at $\sqrt{s}=1.96\mathrm{TeV}$ utilizing data corresponding to an integrated luminosity of $5.3{\mathrm{fb}}^{-1}$ collected with the D0 detector at the Fermilab Tevatron Collider. We consider final states containing one high-$p_T$ isolated electron or muon and at least two jets, and we perform three analyses: one exploiting specific kinematic features of $t\overline{t}$ events, the second using $b$-jet identification, and the third using both techniques to separate the $t\overline{t}$ signal from the background. In the third case, we determine simultaneously the $t\overline{t}$ cross section and the ratio of the production rates of $W+\mathrm{\text{heavy}}$ flavor jets and $W+\mathrm{\text{light}}$ flavor jets, which reduces the impact of the systematic uncertainties related to the background estimation. Assuming a top quark mass of 172.5 GeV, we obtain ${\sigma }_{t\overline{t}}={7.78}_{-0.64}^{+0.77}\mathrm{pb}$. This result agrees with predictions of the standard model.

Figure 1

Distributions of input variables used in the RF discriminant for the $\ell +>3\mathrm{\text{jets}}$ channel in data overlaid with the predicted background and $t\overline{t}$ signal calculated using ${\sigma }_{t\overline{t}}=7.78\mathrm{pb}$ as measured using the combined method. Contributions of the $e+\mathrm{\text{jets}}$ and $\mu +\mathrm{\text{jets}}$ channels are summed.

Figure 2

Output of the RF discriminant for (a) and (b) $\ell +2\mathrm{\text{jets}}$, (c) and (d) $\ell +3\mathrm{\text{jets}}$, and (e) and (f) $\ell +>3\mathrm{\text{jets}}$ events, for backgrounds and a $t\overline{t}$ signal based on the cross section obtained with the kinematic method. The ratio of data over MC prediction is also shown. The left plots (a), (c), and (e) show the results with the nuisance parameters fixed at a value of zero. The right plots (b), (d, and (f) show the results when the nuisance parameters are determined simultaneously with the $t\overline{t}$ cross section in the fit. In the left and right plots the contribution from the $t\overline{t}$ signal is normalized to the results of the cross section measurement, ${\sigma }_{t\overline{t}}=7.00$ and 7.68 pb, respectively. Contributions of the $e+\mathrm{\text{jets}}$ and $\mu +\mathrm{\text{jets}}$ channels are summed.

Figure 3

Distributions of events with 0, 1, and $>1$ $b$-tagged jets for (a) $\ell +3\mathrm{\text{jets}}$ and (b) $\ell +>3\mathrm{\text{jets}}$, for backgrounds and contributions from $t\overline{t}$ signal for ${\sigma }_{t\overline{t}}=8.13\mathrm{pb}$ as measured using the $b$-tagging method. Contributions of the $e+\mathrm{\text{jets}}$ and $\mu +\mathrm{\text{jets}}$ channels are summed.

Figure 4

Output of the RF discriminant for (a) $\ell +3\mathrm{\text{jets}}$, (b) $\ell +>3\mathrm{\text{jets}}$ for events without $b$-tagged jets, and (c) $\ell +3\mathrm{\text{jets}}$ with one $b$-tagged jet, for backgrounds and contributions from the $t\overline{t}$ signal for a cross section of 7.78 pb as measured with the combined method. Contributions of the $e+\mathrm{\text{jets}}$ and $\mu +\mathrm{\text{jets}}$ channels are summed.

Figure 5

Jet multiplicity distributions for events with (a) 0, (b) 1, and (c) $>1$ $b$-tagged jets for backgrounds and contributions from the $t\overline{t}$ signal for a cross section of 7.78 pb as measured with the combined method. Contributions of the $e+\mathrm{\text{jets}}$ and $\mu +\mathrm{\text{jets}}$ channels are summed.

Figure 6

Experimental and theoretical [1, 2, 4] values of ${\sigma }_{t\overline{t}}$ as a function of $m_t$. The point shows ${\sigma }_{t\overline{t}}$ measured using the combined method, the black line shows the fit with Eq. (10), and the gray band with its dashed delimiting lines shows the corresponding total experimental uncertainty. Each curve is bracketed by dashed lines of the corresponding color that represent the theoretical uncertainties due to the choice of PDF and the renormalization and factorization scales (added linearly).