Partonic cross section generation

Many programmes exist to evaluate partonic cross sections. Some are general purpose, such as MadGraph5_aMC@NLO and MCFM, in that they compute predictions for a variety of physical processes (e.g. drell-yan production, single top production, …) up to a given order. Others are more specific, such as top++, which makes predictions for top quark pair production only. Some of these programmes will be briefly outlined here. Note that to produce predictions at NNLO in QCD, which is the highest order used in NNPDF fits, one usually produces APPLgrids at NLO in QCD, and then supplements these with NNLO QCD corrections which are computed with a code with NNLO capabilities. These C-factors are often provided to the collaboration by external parties, rather than the code being run in-house.

MadGraph5_aMC@NLO is the programme that will be used for most of the future NNPDF calculations of partonic cross sections. This is in large part due to its ability to compute predictions at NLO in QCD with NLO EW corrections. To generate APPLgrids from MadGraph5_aMC@NLO, one can use aMCfast, which interfaces between the two formats.

Other codes

MCFM (‘Monte Carlo for FeMtobarn processes’) is an alternative programme to MadGraph5_aMC@NLO, which instead uses mcfm-bridge as an interface to generate APPLgrids.

FEWZ (‘Fully Exclusive W and Z Production’) is a programme for calculating (differential) cross sections for the Drell-Yan production of lepton pairs up to NNLO in QCD.

NLOjet++ is a programme that can compute cross sections for a variety of processes up to NLO. The processes include electron-positron annihilation, deep-inelastic scattering (DIS), photoproduction in electron-proton collisions, and a variety of processes in hadron-hadron collisions.

Top++ is a programme for computing top quark pair production inclusive cross sections at NNLO in QCD with soft gluon resummation included up to next-to-next-to-leading log (NNLL).