Measurement of the integrated and differential $t\overline{t}$ production cross sections for high-$p_{\mathrm{T}}$ top quarks in $pp$ collisions at $\sqrt{s}=8\mathrm{TeV}$

The cross section for pair production of top quarks ($t\overline{t}$) with high transverse momenta is measured in $pp$ collisions, collected with the CMS detector at the LHC with $\sqrt{s}=8\mathrm{TeV}$ in data corresponding to an integrated luminosity of $19.7{\mathrm{fb}}^{-1}$. The measurement is performed using $\mathrm{lepton}+\text{jets}$ events, where one top quark decays semileptonically, while the second top quark decays to a hadronic final state. The hadronic decay is reconstructed as a single, large-radius jet, and identified as a top quark candidate using jet substructure techniques. The integrated cross section and the differential cross sections as a function of top quark $p_{\mathrm{T}}$ and rapidity are measured at particle level within a fiducial region related to the detector-level requirements and at parton level. The particle-level integrated cross section is found to be ${\sigma }_{t\overline{t}}=0.499\pm 0.035(\mathrm{stat}+\mathrm{syst})\pm 0.095(\mathrm{theo})\pm 0.013(\mathrm{lumi})\mathrm{pb}$ for top quark $p_{\mathrm{T}}>400\mathrm{GeV}$. The parton-level measurement is ${\sigma }_{t\overline{t}}=1.44\pm 0.10(\mathrm{stat}+\mathrm{syst})\pm 0.29(\mathrm{theo})\pm 0.04(\mathrm{lumi})\mathrm{pb}$. The integrated and differential cross section results are compared to predictions from several event generators.

Figure 1

Lepton $|\eta |$ and $m_{\mathrm{vtx}}$ distributions from data (points) and for signal and background sources (histograms) with normalizations from the fit for the 0t (top), $1\mathrm{t}+0\mathrm{b}$ (middle), and $1\mathrm{t}+1\mathrm{b}$ (bottom) event categories, for the $e+\text{jets}$ (left column) and $\mu +\text{jets}$ (right column) channels. The vertical bars on the data points represent the statistical uncertainties. The shaded bands reflect the combined statistical and experimental systematic uncertainties after the fit to the signal and background yields, added in quadrature neglecting their correlations for presentational purposes. The ratios of data ($N_{\text{Data}}$) to the total prediction from the fit ($N_{\mathrm{Fit}}$) are shown below each panel, along with the uncertainty band from the fit.

Figure 2

Transverse momentum (left column) and rapidity (right column) distributions of the hadronic-side, large-$R$ jet for the 0t (top), $1\mathrm{t}+0\mathrm{b}$ (middle), and $1\mathrm{t}+1\mathrm{b}$ (bottom) event categories, combining the $e+\text{jets}$ and $\mu +\text{jets}$ channels. The data are compared to the total signal and background yields using normalizations from the maximum-likelihood fit. The vertical bars on the data points represent the statistical uncertainties. The shaded bands reflect the combination of the statistical and post-fit systematic uncertainties in the signal and background yields added in quadrature, without the uncertainties based on the form of the distributions, and neglecting their correlations for presentational purposes. The ratios of data ($N_{\text{Data}}$) to the total prediction from the fit ($N_{\mathrm{Fit}}$) are shown below each panel, along with the uncertainty band from the fit.

Figure 3

Differential $t\overline{t}$ cross section in bins of particle-level $t$ jet $p_{\mathrm{T}}$ (top left), parton-level top quark $p_{\mathrm{T}}$ (top right), particle-level $t$ jet $y$ (bottom left), and parton-level top quark $y$ (bottom right), including all systematic uncertainties. The lower plots show the ratio of the theoretical predictions to the data. The statistical uncertainties are represented by the inner vertical bars with ticks and the light bands in the ratios. The combined uncertainties are shown as full vertical bars and the dark solid bands in the ratios.

Figure 4

Total systematic uncertainties (cross-hatched regions), as well as individual contributions and statistical-only uncertainties (points) in percent as a function of particle-level $t$ jet $p_{\mathrm{T}}$ (top left), parton-level top quark $p_{\mathrm{T}}$ (top right), particle-level $t$ jet $y$ (bottom left), and parton-level top quark $y$ (bottom right) for the differential cross section measurements. The horizontal bars on the points show the bin widths.

Figure 5

Differential $t\overline{t}$ cross section in bins of parton-level top quark $p_{\mathrm{T}}$ including all systematic uncertainties. The measured cross section is compared to theoretical calculations at NNLO for three different PDF sets [52] and at aNNNLO [56]. The lower plot shows the ratio of these theoretical predictions to the data. The statistical uncertainties are represented by the inner vertical bars with ticks and the light bands in the ratios. The combined uncertainties are shown as full vertical bars and the dark solid bands in the ratios.