Measurement of the integrated and differential $t \bar t$ production cross sections for high-$p_T$ top quarks in $pp$ collisions at $\sqrt s =$ 8 TeV

Abstract

The cross section for pair production of top quarks $(t\bar{t})$ with high transverse momenta is measured in pp collisions, collected with the CMS detector at the LHC with $\sqrt{s} =$ 8 TeV in data corresponding to an integrated luminosity of 19.7 fb$^{-1}$. The measurement is performed using lepton+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 $p_T$ 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 $\sigma_{t\bar{t}} =$ 0.499 $\pm$ 0.035 (stat+syst) $\pm$ 0.095 (theory) $\pm$ 0.013 (lumi) pb for top quark $p_T$ > 400 GeV. The parton-level measurement is $\sigma_{t\bar{t}} =$ 1.44 $\pm$ 0.10 (stat+syst) $\pm$ 0.29 (theory) $\pm$ 0.04 (lumi) pb. The integrated and differential cross section results are compared to predictions from several event generators