​2011 IPMU-YITP on Monte Carlo Tools for the LHC, Yukawa Institute for Theoretical Physics, Kyoto, 5-10 Sep 2011

Authors

• Rikkert Frederix (lecturer)
• Claude Duhr (lecturer)

References

• ​QCD and Collider Physics by Keith Ellis, James Stirling, Bryan Webber (Cambridge Monographs, 1996).
• ​Perspectives on LHC physics, Ed. by G. Kane and A. Pierce.
• ​Pythia 6 Physics and Manual (excellent introduction to event generation, parton showers and hadronization).

Exercises 1: Familiarize with MadGraph

• Logon to the MadGraph web site and register: ​http://madgraph.hep.uiuc.edu.
• Register with a valid e-mail address
• Download the latest version of the MadGraph v5 code from the Dowloads page on the madgraph website.
• Untar it and start the command line interface by executing =./bin/mg5=
• Start the tutorial by typing {{{

tutorial }}} in the mg5 command prompt and follow the instruction. Discuss the results with your neighbours.

Exercises 2: Implement a new model with FeynRules

• Read the tutorial sheet Tutorial.pdf​ and follow the instructions together with your neighbours. If you don't have Mathematica, you can download the model files here​ and jump directly to corresponding section of the tutorial sheet.

Extra exercises 1: On-line process generation

• Use the on-line website to 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.

Extra 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, H > e+ ve mu- vm~ (in HEFT model)
• p p > W+ W-, W+>e+ ve, W- > mu- vm~ (important background to previous process)

Extra exercises 3: The full simulation chain and advanced features

Try out the Analysis Tools:

• a Fortran-based package: MadAnalysis (​Download it here)
• a Root-based package: ExRootAnalysis (​Download it here)

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 $
2. • Signal

Events: Parton Level​

Detector Level​

Plots: Parton Level​

Detector Level​

• Background

Events: Parton Level​ <span style="color: #000000;">

</span>Detector Level​

Plots: Parton Level​ <span style="color: #000000;">

</span>Detector Level​

1. Top associated production $pp \to t\bar tH$ with $H \to b \bar b$
   • Signal + Background samples:

Events: Parton Level​

Detector Level​

Plots: Parton Level​

Detector Level​

Extra exercises 4: Implementation of a new model in MadGraph or ​FeynRules + MadGraph

• Implement your favourite Model into MadGraph using FeynRules, specific for studying a given process. Generate events, study relevant distributions.
• Determine most relevant Standard Model backgrounds with identical final states (&ldquo;non-reducible&rdquo;). If not too complicated, generate backgrounds with cuts determined from signal distributions.
• Which other (&ldquo;reducible&rdquo;) backgrounds might be important?
• Can the signal be seen at Tevatron? At the LHC?

Animations

• ​Interactive Flash version Note you may want to zoom in!
• ​Fast movie (.avi) of collision
• ​Guided movie (.mov) of collision
• ​John Ellis on Daily Show