# Measurement of double-differential cross sections for top quark pair production in pp collisions at sqrt(s) = 8 TeV and impact on parton distribution functions

## TL;DR

This paper measures double-differential cross sections for top quark pair production at 8 TeV in proton-proton collisions, compares results with QCD predictions, and demonstrates the impact on refining parton distribution functions, especially the gluon distribution.

## Contribution

It provides new precise measurements of top quark pair production cross sections and shows their significant impact on improving the gluon distribution in parton distribution functions.

## Key findings

- Overall agreement with QCD predictions, improved with latest PDFs
- Measurement constrains gluon distribution in the proton
- Data enhances the accuracy of parton distribution functions

## Abstract

Normalized double-differential cross sections for top quark pair (t t-bar) 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 inverse femtobarns. The measurement is performed in the dilepton e+/- mu-/+ final state. The t t-bar cross section is determined as a function of various pairs of observables characterizing the kinematics of the top quark and t t-bar 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 t-bar cross sections in a fit of parametrized parton distribution functions is shown to have significant impact on the gluon distribution.