ROOT Analysis Framework (I) Introduction. Qipeng Hu March 15 th, 2015

Transcription

1 ROOT Analysis Framework (I) Introduction Qipeng Hu March 15 th, 2015

2 What is ROOT? Why do we use it? Simple answer: It makes plots!

3 Graph [fb/gev] dσ jet /de T,jet s = 14 TeV η <0.5 jet Data 2009 NLO QCD sin(y)*sin(x)/(x*y) ATLAS Preliminary E T,jet [GeV] Full Corrected Events ATLAS Internal 2013 p+p, Ldt = 4 pb s = 2.76 TeV Function Histogram - µ + µ y 3

4 What is ROOT? ROOT is an Object-Oriented analysis framework. User-compiled code can be called to produce graphics, perform fits and calculate statistics. Event Data Data Detector Event Generators Simulation Reconstruction Acquisition Analysis ROOT Framework 4

5 Why is ROOT? It knows about tree (n-tuples), histograms, 4-vector, detector geometry, function-fitting and multi-variable analysis etc. It can handle large volumes of data (millions of physics events; files of GB~TB in size) Multi-platform (Windows, Mac, may UNIX flavors) It s free! 5

6 ROOT analysis A typical ROOT analysis could be: Save data Access data Analyze data Show results 6

7 How to run ROOT Start ROOT: - source setup script./root_dir/bin/thisroot.sh - type root in the terminal Welcome to ROOT 6.02/02 (c) , The ROOT Team Built for macosx64 From tag v , 26 November 2014 Try '.help', '.demo', '.license', '.credits', '.quit'/'.q' root [0] - Quit ROOT root [0].q 7

8 Walkthrough: Plotting a function TF1 class contains all utilities one needs to play with functions. TF1* f1 = new TF1("f1","sin(x)/x",0,); f1->draw(); construct function TF1* funcname = new TF1( funcname, TMath::formula,x_low,x_high); TF2* f2 = new TF2("f2","sin(y)*sin(x)/(x*y)",-,,-,); f2->draw("surf1"); There re several draw options for 2D plots: surf*, cont*, colz, box 8

9 Walkthrough: Histograms TH1 class contains all utilities one needs to play with functions. TH1F* histname = new TH1F( histname, title,n_bins,x_low,x_high); construct function TH1F* h1 = new TH1F("h1","Histogram from a gaussian",0,-3,3); h1->fillrandom("gaus",000); h1->draw(); h1->fit("gaus"); 9

10 What are we talking about, when we talk about trees? Tree (TTree) class is a utility for saving and accessing HEP event data. event #1 event #2 event #3 event index muon number muon pt electron number This is a p+p collision event in human understanding

11 Anatomy of a tree Branches Entries event index event #1 event #2 int event #3 If there re 5 muons in event #2, muon number should be 5 and muon pt should be a vector of 5 in size. To analyze this tree, one can use loops like: muon number muon pt int vector <float> Loop over event entries { Loop over muons{ some computation } Loop over electrons { some computation } } 11

12 Walkthrough: trees (ii) Simple analysis using the Draw command TFile* myflie = new TFile("example.root","READ"); TBrowser tb SkimmedD3PD->Draw("mu_pt","mu_pt > 000 && mu_pt < 50000") 12

13 Analyze a tree using C++ Analyze TTree using C++: SkimmedD3PD->MakeClass("ana") Files called ana.c and ana.h would be generated. #ifndef ana_h #define ana_h class ana { public : ana(ttree *tree=0); virtual ~ana(); virtual Int_t Cut(Long64_t entry); virtual Int_t GetEntry(Long64_t entry); virtual Long64_t LoadTree(Long64_t entry); virtual void Init(TTree *tree); virtual void Loop(); virtual Bool_t Notify(); }; #endif virtual void Show(Long64_t entry = -1); ana is now a C++ Class! 13

14 if (fchain == 0) return; Long64_t nentries = fchain->getentriesfast(); TH1F* h_mass = new TH1F("h_mass","histogram of dimuon mass",0,2.5,3.5); Long64_t nbytes = 0, nb = 0; for (Long64_t jentry=0; jentry<nentries;jentry++) { Long64_t ientry = LoadTree(jentry); if (ientry < 0) break; nb = fchain->getentry(jentry); nbytes += nb; // if (Cut(ientry) < 0) continue; if (mu_n!=2) continue; for (int i=0; i<mu_n; i++) { TLorentzVector mom_mu1; mom_mu1.setptetaphie(mu_pt->at(i)/00.,mu_eta->at(i),mu_phi->at(i),mu_e- >at(i)/00.); for (int j=i+1; j<mu_n; j++) { TLorentzVector mom_mu2; mom_mu2.setptetaphie(mu_pt->at(j)/00.,mu_eta->at(j),mu_phi- >at(j),mu_e->at(j)/00.); TLorentzVector mom = mom_mu1 + mom_mu2; h_mass->fill(mom.m()); } } } h_mass->draw(); 14

15 Example of fitting in ROOT root -l rf201_composite.c Events / ( 0.1 ) - Build fit model - Parameterization optimization - Test of goodness of fit - Error estimation - Composite visualization Example of composite pdf=(sig1+sig2)+bkg x 15

16 Outlines of this tutorial Basic: Introduction Make your first ROOT plot Analyze ROOT tree in C++ Advanced: Covers UNIX command line, vim editor Covers a brief introduction to C++ Fitting in ROOT Machine Learning in ROOT Related slides and files will be put on Web (under construction), will be available next week. 16

17 Contact information 胡启鹏 近代物理系

18 Thanks

19 Install ROOT ROOT can be downloaded from Install ROOT from source: drupal/content/installing-root-source. Be sure you have all the build prerequisites. (it will take minutes to compile) Binaries are available for Linux SLC5/SLC6, OSX, Windows. 19

20 Useful Links ROOT web-page: Official Tutorials: Tutorials.html. User s Guide. Example macros: $ROOTSYS/tutorial/ 20