MadGraph5_aMC@NLO

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MadGraph5_aMC@NLO is an event generator.

This event generator can do multiple type of computation

  • LO cross-section computation and event generation (tree level and loop induced processes)
  • NLO fix order computation
  • NLO+PS computation (via the MC@NLO method)

Those type of computation are available for the SM and for a large class of model via the UFO format.

The package also include a lot of additional feature

  • matrix-element provider (tree level and one loop)
  • MadSpin (decay of massive particle in the NWA limit)
  • Systematics a code for computation of theoretical uncertainties via re-weighting
  • Re-weighting a code to reuse a sample of events (LO OR NLO) and change the weight of each event to predict the shape of a new BSM/SM benchmark

External package can also be interfaced to MadGraph5_aMC@NLO (you can use the "install" command to install those)

  • maddm : tools for DM computation (relic density, direct detection,...)
  • pythia8 : allow to automatically shower your sample as soon as they are generated
  • madanalysis5: analysis and recasting tool
  • Delphes: Detector simulation (fast sim)
  • ExRootAnalysis: convert your LHE file to root
  • NINJA/COLLIER: Additional package to speed up loop computation

Process selection

The definition of a physical process to generate supports the following syntax, shown by example of the process pp \to e^+e^-:

p p > z > e+ e-       # requires one s-channel z (but doesn't require it to be on-shell)
p p > z, z > e+ e-    # on-shell z decaying
p p > e+ e- $ z       # forbids s-channel z to be on-shell)
p p > e+ e- $$ z      # forbids any z in s-channel
p p > e+ e- / z       # forbids any z

Usage in ATLAS

Instructions for using MadGraph5_aMC@NLO in the ATLAS software can be found here (internal).

As MG5_aMC@NLO can run in both LO and NLO modes the naming convention for samples is not entirely obvious. So we make the choice to use the following convention:

  • LO process (MadGraph or MG5_aMC@NLO) = "MadGraph" or short "MG"
  • NLO process (aMC@NLO or MG5_aMC@NLO) = "aMcAtNlo" or short "aMC"

This convention should be maintained at every stage of the MC production chain – i.e LHE file inputs, JOs, evgenConfig.generators, etc. But it should be noted that the generator should still formally be referred to as MadGraph5_aMC@NLO, the sample naming convention is for our internal ATLAS convenience, to easily distinguish between LO and NLO samples.

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