Constraints on the gluon PDF from top quark pair production at hadron colliders

TL;DR

This paper uses NNLO calculations and collider data to constrain the gluon parton distribution function, reducing uncertainties and improving predictions for Standard Model and Beyond Standard Model processes at the LHC.

Contribution

It provides the first comprehensive NNLO+NNLL analysis incorporating top quark data to refine the gluon PDF at large x, with implications for new physics predictions.

Findings

Top quark pair production constrains the gluon PDF at large x.

Reduced gluon PDF uncertainties improve BSM process predictions.

Updated NNLO+NNLL predictions for top cross section ratios and heavy quark production.

Abstract

Using the recently derived NNLO cross sections \cite{Czakon:2013goa}, we provide NNLO+NNLL theoretical predictions for top quark pair production based on all the available NNLO PDF sets, and compare them with the most precise LHC and Tevatron data. In this comparison we study in detail the PDF uncertainty and the scale, $m_t$ and $\alpha_s$ dependence of the theoretical predictions for each PDF set. Next, we observe that top quark pair production provides a powerful direct constraint on the gluon PDF at large $x$, and include Tevatron and LHC top pair data consistently into a global NNLO PDF fit. We then explore the phenomenological consequences of the reduced gluon PDF uncertainties, by showing how they can improve predictions for Beyond the Standard Model processes at the LHC. Finally, we update to full NNLO+NNLL the theoretical predictions for the ratio of top quark cross sections between different LHC center of mass energies, as well as the cross sections for hypothetical heavy fourth-generation quark production at the LHC.