Models ExperimentModels ExperimentBridging the GapBridging the Gap

Tim StelzerTim Stelzer

Fabio Maltoni + CPFabio Maltoni + CP33

OutlineOutline

Anatomy of an EventAnatomy of an Event

Parton Shower MCParton Shower MC

Matrix Element CorrectionsMatrix Element Corrections

Current ToolsCurrent Tools

OutlookOutlook

A Top Quark EventA Top Quark Event

1. High-Q Scattering2 2. Parton Shower

3. Hadronization 4. Underlying Event

Anatomy of an Event

1. High-Q Scattering2 2. Parton Shower

3. Hadronization 4. Underlying Event

☞ Where new physics lies

☞ process dependent

☞ first principles description

☞ it can be systematically improved

Hard Scattering

1. High-Q Scattering2 2. Parton Shower

3. Hadronization 4. Underlying Event

☞ QCD -”known physics”

☞ universal/ process independent

Parton Shower

1. High-Q Scattering2 2. Parton Shower

3. Hadronization 4. Underlying Event

universal/ process independentmodel dependent

☞ low Q physics2

Hadronization

1. High-Q Scattering2 2. Parton Shower

3. Hadronization 4. Underlying Event

☞ energy and process dependent ☞ model dependent

☞ low Q physics2

Underlying Event

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Parton Shower MCParton Shower MCHERWIG / PythiaHERWIG / Pythia

ME involving q →q g ( or g → gg) are strongly enhanced when they are close in the phase space:

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1-z

Mp

Collinear factorization:

Start with Hard Process* then allow to radiate

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Tevatron to LHCTevatron to LHC BackgroundsBackgrounds

Multi-parton (tt)Multi-parton (tt) Study firstStudy first Key to SignalKey to Signal

Require better Require better event generatorsevent generators

Improve Hard Scattering Improve Hard Scattering

1. Identify all suprocesses (gg-> ggg, gq -> ggq, etc) in

2. For each one calculate amplitude

3. Square amplitude, sum over spins & color, integrate over phase space

Easy

Hard

Very hard

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HERWIG / PYTHIA

Matching

1. hadron-level description1. parton-level description

ME Shower MC

2. fixed order calculation 2. resums large logs

4. valid when partons are hard and well separated

4. valid when partons are collinear and/or soft

5. needed for realistic studies

Approaches are complementary!

But double-counting has to be avoided!

3. quantum interference exact 3. quantum interference through AO

5. needed for multi-jet description

M.E. / Shower MatchingM.E. / Shower Matching

Avoid Double CountingAvoid Double Counting

1. The most inclusive observable.2. All parton multiplicities contribute.3. Excellent agreement with TeV data (validation)

[J. Alwall]Matching ResultsMatching Results

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HERWIG / PYTHIACKKW, MLMFe

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Available ToolsAvailable Tools Showering/HadronizationShowering/Hadronization

HERWIGHERWIG PythiaPythia SHERPA SHERPA

Hard ScatteringHard Scattering Alpgen (Multi parton)Alpgen (Multi parton) AMEGIC (SHERPA integration)AMEGIC (SHERPA integration) Comphep/Calchep (User Interface)Comphep/Calchep (User Interface) MadGraph/MadEvent (see next slide)MadGraph/MadEvent (see next slide)

MadEvent PhilosophyMadEvent Philosophy

Remove gap Theory and ExperimentRemove gap Theory and Experiment

Versatile: Single MC for SM Versatile: Single MC for SM background and New Physicsbackground and New Physics

Modular: Add New Model/CalculatorModular: Add New Model/Calculator

Low Learning Curve (Web Based)Low Learning Curve (Web Based)

Open: (Vista, MARMOSET, Bridge)Open: (Vista, MARMOSET, Bridge)

StructureStructure

Models in MadGraph

- MSSM Rainwater+Plehn+Alwall

- Higgs EFTFrederix

-New: General framework for user-defined models

- General 2 Higgs DoubletModel (including CPV)Herquet, De Visscher

- Standard Model

interactions.dat

particles.dat

MadGraph/Sherpa/Whizard SUSY comparison[Hagiwara et al. 2005]

~500 processes to check all Feynman ~500 processes to check all Feynman rules (CP and R-conserving, rules (CP and R-conserving,

CKM=MSN=1)CKM=MSN=1)

Coming SoonComing Soon

New Tools for Adding New ModelsNew Tools for Adding New Models Decay ChainsDecay Chains

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SummarySummary

Accurate simulation of SM Accurate simulation of SM backgrounds and New Physics is backgrounds and New Physics is essential for LHCessential for LHC

Significant progress has been made Significant progress has been made in last 5 yearsin last 5 years

New era in communication between New era in communication between Model builders and experimentalistsModel builders and experimentalists