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

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Timeline 2:00-5:45 2:20 Introduction ----- 20 2:35 Activity 1------ Login+Check ---- 15 2:55 Activity 2------ Download+plot---- 20 3:15 Break (short) Walk to main room 3:20 Generating Events ---- 20 + Running at home 3:30 Activity 3----- SDE check ---- 10 3:35 Running at home --- 5 3:55 Activity 4 --- Download and Run MadEvent.tar.gz 20 4:15 Break 4:20 Decays --- 5 4:35 Activity 5 --- Decay signal events --- 15 4:55 Activity 6 ---- Download background events place cuts ---20 5:00 Conclusions --- 5

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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

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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

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

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

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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

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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

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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

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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

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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 video here 33

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

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Activity 1: Generate pp > h >ttbb~ Predict subprocess/diagrams –e.g. uu~ > bb~ tt~ Open http://madgraph.hep.uiuc.edu/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 Generate Process Benchmark Cross section Download Analysis 45

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Activity 2 Cross Section + Plots Results and Event Database –Check Cross Section –Download events.dat –Plot events on your machine Generate Process Benchmark Cross section Download Analysis 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

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Let’s go do it!

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

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

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For strong cuts, |a 1 +a 2 | 2 ≈ 1 (Pt > 90, R > 1.0) Example: u ve -> g u ve 18

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

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

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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 Single Diagram Enhanced MadEvent 30

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MadEvent Example Vector Bosons 31

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MadEvent Example Heavy Quarks 32

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

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More Checks…..

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

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

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Activity 3 Run Check using SDE Check Cross Section Details –(10 minutes) – (dd~) = (d~d) G1 = G2 –gg_tt~bb~ G1 = G2 = G4 = G5 G3 = G6 G11 = G12 Generate Process Benchmark Cross section Download Analysis 47

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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

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Activity 4: Run on your machine 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 Generate Process Benchmark Cross section Download Analysis Work/Break start again at 4:30

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

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

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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

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

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

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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…) MadEvent Summary 25

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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)

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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!

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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

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

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

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Signal pp>h>tt~bb~ Generation –setcuts.f (run_cuts.dat) E t, R, M ij –setparams.f PDF, Scales, Collider Analysis –plot_events.f Easy secondary cuts –Decay Decay unstable particles in events.dat Generate Process Benchmark Cross section Download Estimate Uncertainty Analysis

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Activity 4: Download and Run Event Generator Download Code madevent.tar.gz Generate Process Benchmark Cross section Download Analysis 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

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Background Download events Select cuts to improve Signal/Background –90 < M bb < 150 emacs Source/plot_events.f

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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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