Measurement of the $t\overline{t}$ production cross section in $pp$ collisions at 7 TeV in $\mathrm{\text{lepton}}+\mathrm{\text{jets}}$ events using $b$-quark jet identification

A new measurement of the inclusive production cross section for $pp\to t\overline{t}$ is performed at a center-of-mass energy of 7 TeV using data collected by the CMS experiment at the LHC. The analysis uses a data sample corresponding to an integrated luminosity of $36{\mathrm{pb}}^{-1}$, and is based on the final state with one isolated, high transverse momentum muon or electron, missing transverse energy, and hadronic jets. The $t\overline{t}$ content of the selected events is enhanced by requiring the presence of at least one jet consistent with $b$-quark hadronization. The measured cross section is $150\pm 9(\mathrm{stat})\pm 17(\mathrm{syst})\pm 6(\mathrm{lumi})\mathrm{pb}$ and is in agreement with higher-order QCD calculations. The combination of this measurement with a previous CMS result based on dileptons gives $154\pm 17(\mathrm{stat}+\mathrm{syst})\pm 6(\mathrm{lumi})\mathrm{pb}$.

Figure 1

Secondary vertex mass distribution for bottom, charm, and light flavor jets. The bottom and charm templates are taken from simulated $t\overline{t}$ events and the light flavor shape is taken from simulated $W+\mathrm{\text{jet}}$ events.

Figure 2

Results of the combined muon and electron channel fit. The muon channel is shown on the left and the electron channel on the right. The plots on the top are for exactly 1 $b$ tag and those on the bottom are for $\ge 2$ $b$ tags. The histograms within the top panel correspond to events with 1, 2, 3, 4 and $\ge 5\mathrm{\text{jets}}$, respectively, while the bottom panel shows histograms corresponding to events with 2, 3, 4 and $\ge 5\mathrm{\text{jets}}$.

Figure 3

Kinematic distributions of the total transverse energy ($H_T$), the missing transverse energy ($E_T^{\mathrm{miss}}$) and the transverse mass of the $W$ (${\mathrm{E̸}}_T$). The plots are for $\ge 3\mathrm{\text{jets}}$ and $\ge 1b$ tag and the comparison histograms correspond to the fitted values. The muon channel is shown on the left and the electron channel is on the right.

Figure 4

Results of the template fit to the neural-network discriminant for $36{\mathrm{pb}}^{-1}$ of data.

Figure 5

Comparison of data and simulation for the jet-multiplicity for events with $\ge 1$ muon-in-jet-tag. The $W+\mathrm{\text{jets}}$ and QCD contributions are normalized to the data-driven predictions. The hatched area shows total uncertainty on the background prediction.

Figure 6

Number of observed and predicted secondary vertex tags in events with $\ge 3\mathrm{\text{jets}}$.

Figure 7

Comparison of the CMS measurements for the $t\overline{t}$ production cross sections and the QCD predictions for $\sqrt{s}=7\mathrm{TeV}$.

Figure 8

Comparison of the CMS and Tevatron results for the $t\overline{t}$ production cross section with QCD as a function of $\sqrt{s}$.