Parton distributions from LHC, HERA, Tevatron and fixed target data: MSHT20 PDFs

S Bailey,R S Thorne,T Cridge,L A Harland-Lang,A D Martin

doi:10.1140/epjc/s10052-021-09057-0

Abstract

We present the new MSHT20 set of parton distribution functions (PDFs) of the proton, determined from global analyses of the available hard scattering data. The PDFs are made available at NNLO, NLO, and LO, and supersede the MMHT14 sets. They are obtained using the same basic framework, but the parameterisation is now adapted and extended, and there are 32 pairs of eigenvector PDFs. We also include a large number of new data sets: from the final HERA combined data on total and heavy flavour structure functions, to final Tevatron data, and in particular a significant number of new LHC 7 and 8 TeV data sets on vector boson production, inclusive jets and top quark distributions. We include up to NNLO QCD corrections for all data sets that play a major role in the fit, and NLO EW corrections where relevant. We find that these updates have an important impact on the PDFs, and for the first time the NNLO fit is strongly favoured over the NLO, reflecting the wider range and in particular increased precision of data included in the fit. There are some changes to central values and a significant reduction in the uncertainties of the PDFs in many, though not all, cases. Nonetheless, the PDFs and the resulting predictions are generally within one standard deviation of the MMHT14 results. The major changes are the u-d valence quark difference at small x, due to the improved parameterisation and new precise data, the {bar{d}}, {bar{u}} difference at small x, due to a much improved parameterisation, and the strange quark PDF due to the effect of LHC W, Z data and inclusion of new NNLO corrections for dimuon production in neutrino DIS. We discuss the phenomenological impact of our results, and in general find reduced uncertainties in predictions for processes such as Higgs, top quark pair and W, Z production at post LHC Run-II energies.

Highlights

The parton distribution functions (PDFs) of the proton are determined from fits to the world data on deep inelastic scattering (DIS), and more recently from the rapidly increasing variety of related hard scattering processes at hadron colliders
There have been a number of intermediate updates between the MMHT14 PDFs and the MSHT20 PDFs that we present here
We find no significant improvement in the fit to the HERA heavy flavour structure function data by varying the quark masses, or by changing the unknown parameters in our approximation for the O(αS3) contribution in the fixed flavour number scheme (FFNS)

Summary

Introduction

The parton distribution functions (PDFs) of the proton are determined from fits to the world data on deep inelastic scattering (DIS), and more recently from the rapidly increasing variety of related hard scattering processes at hadron colliders. For examples of the most up-to-date PDFs using a variety of approaches and more or less comprehensive choices of input data see [1,2,3,4,5,6]. It is important to present a major update of the MMHT14 PDFs, to take account of both the improvements and extensions in data and the accompanying improvements in our theoretical framework. We denote these new PDFs by MSHT20

Methods

Results

Conclusion