Abstract
Normalized double-differential cross sections for top quark pair ($t\overline{t}$) production are measured in pp collisions at a centre-of-mass energy of 8 TeV with the CMS experiment at the LHC. The analyzed data correspond to an integrated luminosity of 19.7 $fb^{-1}$. The measurement is performed in the dilepton $e^{\pm }\mu^{\mp}$ final state. The $t\overline{t}$ cross section is determined as a function of various pairs of observables characterizing the kinematics of the top quark and $t\overline{t}$ system. The data are compared to calculations using perturbative quantum chromodynamics at next-to-leading and approximate next-to-next-to-leading orders. They are also compared to predictions of Monte Carlo event generators that complement fixed-order computations with parton showers, hadronization, and multiple-parton interactions. Overall agreement is observed with the predictions, which is improved when the latest global sets of proton parton distribution functions are used. The inclusion of the measured $t\overline{t}$ cross sections in a fit of parametrized parton distribution functions is shown to have significant impact on the gluon distribution.
CMS Collaboration