Measurement of double differential cross sections for top quark pair production in pp collisions at sqrt[s] = 8 TeV

Normalized double differential cross sections for top quark pair ($\rm{t\bar{t}}$) production are measured in $\text{pp}$ 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 $19.7\,{\rm fb}^{-1}$. The measurement is performed using the dilepton ${\rm e}^{\pm}\mu^{\mp}$ decay mode of the $\rm{t\bar{t}}$ system. The $\rm{t\bar{t}}$ cross section is measured as a function of various combinations of two observables characterizing the kinematics of the top quark and the $\rm{t\bar{t}}$ system. The data are compared to calculations in perturbative QCD at next-to-leading order and approximate next-to-next-to-leading order, and to predictions of Monte Carlo event generators that complement fixed-order computations with parton showers, hadronization, and multiple-parton interactions. Overall, a reasonable agreement is observed which is improved when the latest global sets of proton parton distribution functions are used in the predictions. The impact of the measured cross sections constraining the gluon distribution in the proton is demonstrated in a fit of parametrized parton distribution functions to the data.