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Collider Event Generation

NumS-HEP 2011 school, NCTU, Taiwan, 17-23 Jan 2011


  • Johan Alwall (lecturer)


Find the pdf of the 3 x 1.5 hours lectures:


Basic exercises 1: Familiarize with Software.MadGraph

  • Logon to the Software.MadGraph web site and register:
  • Register with a valid e-mail address
  • Feynman diagrams. Generate a few processes (with different QED + QCD couplings) trying to guess which diagrams appear:
    • uu~>tt~
    • gg>tt~
    • gg>tt~h (in SM and HEFT)
    • uu~>tt~bb~
  • Subprocess identification. List all subprocesses contributing to:
    • pp>l+vljj
    • pp>tt~bb~
    • pp>tt~jj
  • Look at the new physics models and check the particle and interactions content.
  • Advanced: Download the MG/ME package and play with the standalone version.

Basic exercises 2: Calculate cross sections and generate events

  • Generate events for a few selected processes (work in groups, pick one each), for Tevatron and LHC energies. Does the cross section scale as you expect?
  • Compare cross sections with the processes of your neighbors. Do they differ as you would expect?
  • Look at the generated plots. Are the distributions as you would expect? Discuss with your neighbors.

Example processes:

  • ttbar production: pp > tt~, QED=0
  • W production: pp > l+vl
  • Z/gamma* production: pp > e+e-
  • g g > (H > e+ ve mu- vm~) (in HEFT model)
  • p p > (W+>e+ ve) (W- > mu- vm~) (important background to previous process)

Advanced exercises 1: The full simulation chain and advanced features

Try out the Analysis Tools:

Study SM Higgs production at the LHC. Choose a channel and investigate signal and background, using either of the packages above:

  1. The 2 lepton + missing Et final state: $ pp \to H\to W^+ W^- \to e^- \bar \nu_e \mu^+ \nu_\mu $
    • Signal
Events: Parton Level
Detector Level
Plots: Parton Level
Detector Level
  • Background
Events: Parton Level
Detector Level
Plots: Parton Level
Detector Level
  1. Top associated production $pp \to t\bar tH$ with $H \to b \bar b$
    • Signal + Background samples:
Events: attachment:ttbb.lhe.gz Parton Level]
Detector Level
Plots: Parton Level
Detector Level

Advanced exercises 2: Implementation of a new model in MadGraph or FeynRules + MadGraph

Note that for these exercises you need to download the MadGraph/MadEvent package (or MadGraph 5 package) and work locally. You need a Fortran compiler (and for MadGraph 5, Python v. 2.6 or 2.7).

For FeynRules download and information, see the FeynRules wiki

  • Implement a (part of a) Standard Model extension into Software.MadGraph, specific for studying a given process. Generate events, study relevant distributions.
  • Determine most relevant Standard Model backgrounds with identical final states (“non-reducible”). If not too complicated, generate backgrounds with cuts determined from signal distributions.
  • Which other (“reducible”) backgrounds might be important?
  • Can the signal be seen at Tevatron? At the LHC?


-- Main.JohanAlwall - 2011-01-17

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