Measurement of differential $t\bar{t}$ production cross sections in $p\bar{p}$ collisions

TL;DR

This work reports differential measurements of $t\bar{t}$ production in $p\bar{p}$ collisions at $\sqrt{s}=1.96$ TeV using the D0 detector with the full Run II data set. It employs a lepton+jets topology with at least four jets and a $b$-tag, a constrained HitFit reconstruction, and regularized unfolding to obtain parton-level $d\sigma/dX$ for $X = m(t\bar{t})$, $|y^{top}|$, and $p_T^{top}$. The results are compared to approximate NNLO/NNLL QCD predictions and to MC generators such as mc@nlo and Alpgen, showing overall agreement within uncertainties and a total cross section near 8 pb. These measurements provide a stringent test of QCD in the top-quark sector and inform modeling of backgrounds for searches of new physics at hadron colliders.

Abstract

The production of top quark-antiquark pair events in $p\bar{p}$ collisions at $\sqrt{s}=1.96$ TeV is studied as a function of the transverse momentum and absolute value of the rapidity of the top quarks as well as of the invariant mass of the $t\bar{t}$ pair. We select events containing an isolated lepton, a large imbalance in transverse momentum, and four or more jets with at least one jet identified to originate from a $b$ quark. The data sample corresponds to 9.7 fb$^{-1}$ of integrated luminosity recorded with the D0 detector during Run II of the Fermilab Tevatron Collider. Observed differential cross sections are consistent with standard model predictions.

Figures (11)

• Figure 1: The $|\cal{S}$$_c|$ versus $\Delta \phi(\mu,$$\not\!\!E_T$$)$ plane for (a) $t\bar{t}$ events and (b) for $W+$jets background events. The selection requirements are indicated by the solid lines.
• Figure 2: Distributions of the MVD $b$ identification output distribution for the $\ell +2$ jets, $\ell +3$ jets and $\ell + \ge 4$ jets data sample in the (a) $e +$jets and (b) $\mu +$jets decay channel. The data are compared to the sum of predicted contributions from signal and background processes. More details on how the sample composition is derived can be found in the text.
• Figure 3: Distributions of (a) the number of jets, (b) the scalar sum of the $p_T$ values of the lepton and jets, (c) $\hbox{$\not\!\! E_T$}\xspace$, and (d) lepton $p_T$ for the $e +$jets final state. The data are compared to the sum of predicted contributions from signal and background processes. The signal contribution is derived employing mc@nlo simulated events normalized to the measured inclusive $t\bar{t}$ cross section of $8.0~\mathrm{pb}$. The highest bin in the histograms is used as an overflow bin. The ratios of data to the sum of the signal and all background contributions are shown in the panels below the distributions. The bands show the $1$ s. d. combined systematic uncertainties on the sum of the signal and background contributions.
• Figure 4: Distributions of (a) the number of jets, (b) the scalar sum of the $p_T$ values of the lepton and jets, (c) $\hbox{$\not\!\! E_T$}\xspace$, and (d) lepton $p_T$ for the $\mu +$jets final state. The data are compared to the sum of predicted contributions from signal and background processes. The signal contribution is derived employing mc@nlo simulated events normalized to the measured inclusive $t\bar{t}$ cross section of $8.0~\mathrm{pb}$. The highest bin in the histograms is used as an overflow bin. The ratios of data to the sum of the signal and all background contributions are shown in the panels below the distributions. The bands show the $1$ s. d. combined systematic uncertainties on the sum of the signal and background contributions.
• Figure 5: Distribution of $\chi^2$ for the best solution with lowest $\chi^2$ for the (a) $e +$jets and (b) $\mu +$jets final states. The data are compared to the sum of predicted contributions from signal and background processes. The signal contribution is derived employing mc@nlo simulated events normalized to the measured inclusive $t\bar{t}$ cross section of $8.0~\mathrm{pb}$. The highest bin in the histograms is used as an overflow bin. The ratios of data to the sum of the signal and all background contributions are shown in the panels below the distributions. The bands show the $1$ s. d. combined systematic uncertainties on the sum of the signal and background contributions.