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MadGraph + MadEvent

MadGraph + MadEvent. +. Automated Tree-Level Feynman Diagram, Helicity Amplitude, and Event Generation. Tim Stelzer Fabio Maltoni. Exciting Time. Data from Tevatron now! Gain experience with real data and analysis now. Data from LHC soon!

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MadGraph + MadEvent

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  1. MadGraph + MadEvent + Automated Tree-Level Feynman Diagram, Helicity Amplitude, and Event Generation Tim Stelzer Fabio Maltoni

  2. Exciting Time • Data from Tevatron now! • Gain experience with real data and analysis now. • Data from LHC soon! • Develop tools/skills necessary to get most out of LHC data when it comes on line • You will be doing the analysis for the next great discoveries! • Strong links between theory and experiment will be essential 10

  3. Outline • Goal: Improve MadGraph/MadEvent • Only 1 thing more useful • Introduction • Signal pp > h > tt~ bb~ • Generating/Checking Processes • Calculating/Checking Cross Sections • Plotting/Analyzing Events • Running on your machines • Decaying Particles • Backgrounds pp> tt~bb~ • Remarks 13

  4. Standard Model News • Good News! • Every prediction is correct! • Bad News :( • Limited ability to “solve” • QCD is problem! • Miracle that can predict so much Standard Model 15

  5. Parton Distribution Functions (Measured) Evolution+Splitting Hard Scattering Showering Fragmentation Hadronization e+ e- 18

  6. Factorization • Key Idea • Result = PDF * Evolution * hard_scatter *showering * hadronization • Each piece is “independent” • Really? • Soft gluons have “long” wavelength, basically can’t “see” hard scattering • Uncertainty • PDF • Factorization Scale • Renormalization Scale • Showering Scales 21

  7. HERWIG + PYTHIA • Contain everything for many processes • Higher energy collisions require new “Hard” processes • Large amount of time/talent devoted to event generation---Need to streamline! 25

  8. Options • Prepackaged event generators • Fixed number of processes implemented • Usually well tested and packaged • Alpgen---Tree Level • MC@NLO --- One Loop • Create your own generator • “Any” process of interest • CompHEP --- trace • MadGraph/MadEvent --- Helicity Amplitude 28

  9. Big Picture • User Requests: • pp -> e+ ve jjj • QCD Order = 3 • QED Order =2 • MadGraph/MadEvent Returns: • List all contributing sub processes • Feynman diagrams for each sub process • Self-Contained Fortran Package • Integrates cross section • Generates unit-weighted events • Les Houches / HERWIG ready Show Demo 33

  10. Steps • Generate Subprocesses/Diagrams • Calculate Benchmark Cross Section • Download to your machine • Events • Event Generator • Perform Analysis 35

  11. Activity 1:Generate pp > h >ttbb~ Generate Process Benchmark Cross section Download Analysis • Predict subprocess/diagrams • e.g. uu~ > bb~ tt~ • Open http://madgraph.hep.uiuc.edu/ • Sign up for account • Username: madgraph • Password: guest • Generate Process • pp > h > ttbb~ QED=2 QCD=2 • Verify Subprocesses and Diagrams 45

  12. Activity 2Cross Section + Plots Generate Process Benchmark Cross section Download Analysis • Results and Event Database • Check Cross Section • Download events.dat • Plot events on your machine 6 1 0.3921316E-04 0.9118800E+02 0.7546772E-02 0.1270000E+00 -2 2 6 -6 5 -5 0 0 1 1 1 1 0 0 2 2 2 2 0 502 502 0 503 0 501 0 0 501 0 503 -1 -1 1 1 1 1 1 -1 -1 1 -1 -1 1 0.25012024368E+02 0.00000000000E+00 0.00000000000E+00 0.25012024368E+02 2 0.47489237575E+04 0.00000000000E+00 0.00000000000E+00 -0.47489237575E+04 3 0.32457365210E+04 0.35739564193E+02 -0.83428604245E+02 -0.32397820027E+04 4 0.57267081534E+03 -0.25236886174E+02 0.96458748768E+02 -0.53631164644E+03 5 0.54994426015E+03 0.31023829244E+02 -0.53539395070E+02 -0.54643174731E+03 6 0.40558418542E+03 -0.41526507264E+02 0.40509250547E+02 -0.40138633668E+03 05

  13. Let’s go do it!

  14. Generating Events Generate Process Benchmark Cross section Download Estimate Uncertainty Analysis • MadEvent “Automatically” Integrates cross sections and generates unweighted events. • Understanding how, can provide important information. • A mini lesson on Monte Carlo 13

  15. Monte Carlo Integration • Advantages • Large numbers of dimensions • Complicated cuts • ONLY OPTION • Event generation • Limitations • Only works for function f(x) ≈ 1 16

  16. Example:u ve -> g u ve • For strong cuts, |a1+a2|2 ≈ 1 (Pt > 90, DR > 1.0) 18

  17. Adaptive M.C. (VEGAS) • Advantages • Grid adjusts to numerically flatten peaks • Flexible • Limitations • Adjusting grid takes time • Peaks must lie on integration variable 22

  18. Multi-Channel M.C. • Advantages • Allows for more complicated peaks • NEXTCALIBUR, WHIZARD • Limitations • Need to calculate all gi values for each point. (slow) • Each phase space channel must be invertible • N coupled equations for a so only works for small number of channels. 25

  19. Single Diagram EnhancedMadEvent • Key Idea • Any single diagram is “easy” to integrate • Divide integration into pieces, based on diagrams • Get N independent integrals • Errors add in quadrature so no extra cost • No need to calculate “weight” function from other channels. • Can optimize # of points for each one independently • Parallel in nature • What about interference? • Never creates “new” peaks, so we’re OK 30

  20. MadEvent ExampleVector Bosons 31

  21. MadEvent Example Heavy Quarks 32

  22. Not only gets an answer, gets the correct one! 35

  23. More Checks…..

  24. SDE Integration • It works! • Interference is included • Looking at diagrams contributions • Gives information about distributions • Gives checks on integration (symmetry) 37

  25. Activity 3 Run Check using SDE Generate Process Benchmark Cross section Download Analysis • Check Cross Section Details • (10 minutes) • Show example • Keep going…. 47

  26. Running at Home • Web Interface Provides • Intuitive Interface ? • Subprocesses and Diagrams • Basic results and events • Download Process to • Customized cuts • Large/Optimized runs • Own the code! • Portability 50

  27. Activity 4:Run on your machine Generate Process Benchmark Cross section Download Analysis • Download the source code • madevent.tar.gz • Edit important files • Source/setparam.f • Collider, Scale and PDF information • SubProcesses/run_cuts.dat • Standard cuts • Generate events • bin/generate_events 5000 0 • Or use bin/survey and bin/refine Work/Break start again at 4:30

  28. Estimating Uncertainty Generate Process Benchmark Cross section Download Analysis • Sources • PDF • Factorization Scale • Hard-Scattering (loops) • as (renormalization scale) NOT 0.965!! 38

  29. Decay_Events Generate Process Benchmark Cross section Download Analysis • MadEvent has decay utility • Includes spin information • Keeps correct cross section • Includes LesHouches info for passing to HERWIG/Pythia** 44

  30. Activity 5: Decay top • Decay t -> bjj • What is cross section • Plot jj mass • Decay t~ > b~ lv • What is cross section • Plot lv mass 58

  31. Backgrounds • “Backgrounds are measured not calculated…..” Tony Liss • Assignment: Write down some backgrounds for ttH. 01

  32. Activity 6: Backgrounds • Predict Subprocesses/diagrams • Generate Diagrams • Check results • Download Events • Determine cross section • 90 < mbb < 150 20

  33. MadEvent Summary • Advantages • Can handle “any” problem • Web interface is convenient/fast • Expandable to MSSM (out this year) • Many Checks • Works for Theorists and Experimentalists • Limitations • W+5 jets (7,000 diagrams w/ hundreds subprocesses) • No loops (yet…) 25

  34. Background pp>tt~bb~ QED • Generate Diagrams • Pp > tt~bb~ /h tells it not to allow Higgs • Check results • dd~ = d~d • uu~ = u~u <> dd~ • gg • Plots (find Z peak)

  35. Status • http://madgraph.physics.uiuc.edu • 500 MHz Pentium w/ 40 Gigabyte disk • Creates Event Generators to download • Lots of “hits” on cite • FNAL, CERN, DESY, U.W., U. Chicago….. • CDF use • W/Z + jets analysis • Photon + jets analysis • Virtual Collider • Future looks promising!

  36. Vision • Add Web based Integration • User inputs cuts/parameters • Code runs in parallel on cpu farm • Returns cross section and events • Advantages • Reduces overhead to getting results • Reduce computing cost by load leveling • Events can easily be shared/stored • Centralize maintenance • Source Code will ALWAYS be Available

  37. To Do: • Add Computers • Add MSSM to MadGraph II • Improve Speed • Phase Space Grid Guess • Helicity Sums • Color Sums • Add Factorization • 10 jet production

  38. Signal pp>h>tt~bb~ Generate Process Benchmark Cross section Download Estimate Uncertainty Analysis • http://madgraph.hep.uiuc.edu/ • Process= pp > h > tt~ bb~ • QCD = 2 QED = 2 • Username = yeti • Password = yeti

  39. Signal pp>h>tt~bb~ Generate Process Benchmark Cross section Download Estimate Uncertainty Analysis • Generation • setcuts.f (run_cuts.dat) • Et, DR, Mij • setparams.f • PDF, Scales, Collider • Analysis • plot_events.f • Easy secondary cuts • Decay • Decay unstable particles in events.dat

  40. Activity 4: Download and Run Event Generator Generate Process Benchmark Cross section Download Analysis • Download Code madevent.tar.gz csh> mkdir pp_h_ttbb csh > cd pp_h_ttbb csh > mv ../madevent.tar.gz . csh> gunzip madevent.tar.gz csh> tar –xvf madevent.tar csh> emacs SubProcesses/run_cuts.dat csh> emacs Source/setparam.f csh> bin/generate_events

  41. Background • Download events • Select cuts to improve Signal/Background • 90 < Mbb < 150 • emacs Source/plot_events.f

  42. Ideas From Tony • Technical How to run • Parameters • Uncertainties pdf, systematic etc • Limitations/assumptions • Backgrounds don’t come from MC come from Data • Built tools, not analysis • Join CDF • Matrix Element and Shower+Matching • Different generators, LO vs NLO

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