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2011 VUB Francqui Chair: LHC Phenomenology


LHC phenomenology: a journey from standard model measurements to new physics discoveries


Fabio Maltoni (lecturer)


Find the pdf of the 5 lectures:


Higgs notebooks

  1. pp>H at LO (1-loop): details of the calculation (Mathematica Notebook) HiggsGG-LO-mtfinite.nb
  2. pp>H at NLO: details of the calculation (Mathematica Notebook) higgsGG-NLO.nb
  3. pp>H at NLO: cross section evaluation for the LHC (Mathematica Notebook+PDF libraries to be compiled) phenHiggs.tar.gz.

A summary of the results can be found in Higgs.pdf.

MC Exercises

Basics : MC101

A short introduction to the techniques of Monte Carlo integration. Exercises proposed during lecture are collected in this Mathematica Notebook: mc101.nb.

Basic exercises 1: Familiarize with MadGraph
  • Logon to the 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 <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
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 MadGraph, 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?


-- Main.FabioMaltoni - 2011-03-25

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