1. Models Experiment Bridging the Gap Tim Stelzer Fabio Maltoni + CP 3

2. Outline Anatomy of an Event Anatomy of an Event Parton Shower MC Parton Shower MC Matrix Element Corrections Matrix Element Corrections Current Tools Current Tools Outlook Outlook

4. A Top Quark Event

5. 1. High-Q Scattering 2 2. Parton Shower 3. Hadronization4. Underlying Event Anatomy of an Event

6. 1. High-Q Scattering 2 2. Parton Shower 3. Hadronization4. Underlying Event ☞ Where new physics lies ☞ process dependent ☞ first principles description ☞ it can be systematically improved Hard Scattering

7. 1. High-Q Scattering 2 2. Parton Shower 3. Hadronization4. Underlying Event ☞ QCD -”known physics” ☞ universal/ process independent Parton Shower

8. 1. High-Q Scattering 2 2. Parton Shower 3. Hadronization4. Underlying Event universal/ process independent model dependent ☞ low Q physics 2 Hadronization

9. 1. High-Q Scattering 2 2. Parton Shower 3. Hadronization4. Underlying Event ☞ energy and process dependent ☞ model dependent ☞ low Q physics 2 Underlying Event

10. Building Bridges Models Phenomenology Experiment Local Parton Hadron Duality Showering Hadroniz..Underlying Feynman Diagrams

11. Parton Shower MC HERWIG / Pythia ME involving q → q g ( or g → gg) are strongly enhanced when they are close in the phase space: z 1-z MpMp Collinear factorization: Start with Hard Process * then allow to radiate

12. Building Bridges Models Phenomenology Experiment Showering Hadroniz..Underlying HERWIG / PYTHIA Feynman Diagrams

13. Tevatron to LHC Backgrounds Backgrounds Multi-parton (tt) Multi-parton (tt) Study first Study first Key to Signal Key to Signal Require better event generators Require better event generators

14. Improve Hard Scattering Improve Hard Scattering 1. 1. Identify all suprocesses ( gg-> ggg, gq -> ggq, etc) in 2. 2. For each one calculate amplitude 3. 3. Square amplitude, sum over spins & color, integrate over phase space Easy Hard Very hard

15. Building Bridges Models Phenomenology Experiment Showering Hadroniz..Underlying HERWIG / PYTHIA Matching

16. 1. hadron-level description 1. parton-level description ME Shower MC 2. fixed order calculation2. 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 Matching

17. Avoid Double Counting

18. 1. The most inclusive observable. 2. All parton multiplicities contribute. 3. Excellent agreement with TeV data (validation) [ J. Alwall] Matching Results

19. Building Bridges Models Phenomenology Experiment Showering Hadroniz..Underlying HERWIG / PYTHIA CKKW, MLM Feynman Diagrams

20. Available Tools Showering/Hadronization Showering/Hadronization HERWIG HERWIG Pythia Pythia SHERPA SHERPA Hard Scattering Hard 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)

21. MadEvent Philosophy Remove gap Theory and Experiment Remove gap Theory and Experiment Versatile: Single MC for SM background and New Physics Versatile: Single MC for SM background and New Physics Modular: Add New Model/Calculator Modular: Add New Model/Calculator Low Learning Curve (Web Based) Low Learning Curve (Web Based) Open: (Vista, MARMOSET, Bridge) Open: (Vista, MARMOSET, Bridge)

22. Structure

23. Models in MadGraph -MSSM Rainwater+Plehn+Alwall -Higgs EFT Frederix -New: General framework for user-defined models -General 2 Higgs Doublet Model (including CPV) Herquet, De Visscher - Standard Model interactions.dat particles.dat

24. MadGraph/Sherpa/Whizard SUSY comparison [Hagiwara et al. 2005] ~500 processes to check all Feynman rules (CP and R-conserving, CKM=MSN=1)

25. Coming Soon New Tools for Adding New Models New Tools for Adding New Models Decay Chains Decay Chains Models Phenomenology Experiment Showering Hadroniz..Underlying HERWIG / PYTHIA Matching Feynman Diagrams

26. Summary Accurate simulation of SM backgrounds and New Physics is essential for LHC Accurate simulation of SM backgrounds and New Physics is essential for LHC Significant progress has been made in last 5 years Significant progress has been made in last 5 years New era in communication between Model builders and experimentalists New era in communication between Model builders and experimentalists