Abstract
Top-quark pair production at the LHC is directly sensitive to the gluon PDF at large x. While total cross-section data is already included in several PDF determinations, differential distributions are not, because the corresponding NNLO calculations have become available only recently. In this work we study the impact on the large-x gluon of top-quark pair differential distributions measured by ATLAS and CMS at sqrt{s}=8 TeV. Our analysis, performed in the NNPDF3.0 framework at NNLO accuracy, allows us to identify the optimal combination of LHC top-quark pair measurements that maximize the constraints on the gluon, as well as to assess the compatibility between ATLAS and CMS data. We find that differential distributions from top-quark pair production provide significant constraints on the large-x gluon, comparable to those obtained from inclusive jet production data, and thus should become an important ingredient for the next generation of global PDF fits.
Highlights
In the case of top-quark pair production, the next-to-next-to leading order (NNLO) QCD corrections to the total cross-section were computed in 2013 [19,20,21]
We find that differential distributions from top-quark pair production provide significant constraints on the large-x gluon, comparable to those obtained from inclusive jet production data, and should become an important ingredient for the generation of global PDF fits
Note that fits of the normalized differential distributions are supplemented by total cross-sections, and that the first column is the result of the HERA-only baseline fit
Summary
In the case of top-quark pair production, the next-to-next-to leading order (NNLO) QCD corrections to the total cross-section were computed in 2013 [19,20,21] This development allowed for the consistent inclusion of the Tevatron and LHC inclusive top-quark pair measurements into a NNLO global PDF fit [22], which demonstrated how this data could help reducing the rather sizable uncertainty of the gluon PDF for x >∼ 0.1. It is natural to investigate how the constraints upon the large-x gluon PDF obtained from inclusive measurements are improved once the additional information contained in the differential distributions is accounted for in a global NNLO analysis (see [27] for a first study based on approximate NNLO) Such a program is enabled by th√e availability of precision measurements of top-quark pair differential cross-sections at s = 8 TeV from ATLAS [28] and CMS [29], provided with the full information on the breakdown of experimental statistical and systematic uncertainties. We demonstrate how differential distributions from top-quark pair production lead to a significant reduction of the gluon PDF uncertainty at large x, and that their impact is comparable to that obtained from inclusive jet measure-
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