Example of analysis class for the H1 data

// Example of analysis class for the H1 data.
// =========================================
//
// This file uses 4 large data sets from the H1 collaboration at DESY Hamburg.
// One can access these data sets (277 MBytes) from the standard Root web site 
// at:       ftp://root.cern.ch/root/h1analysis/
// The Physics plots below generated by this example cannot be produced when
// using smaller data sets.
//
// There are several ways to analyze data stored in a Root Tree
//   -Using TTree::Draw: This is very convenient and efficient for small tasks.
//     A TTree::Draw call produces one histogram at the time. The histogram
//     is automatically generated. The selection expression may be specified
//     in the command line.
//   
//   -Using the TTreeViewer: This is a graphical interface to TTree::Draw
//      with the same functionality.
//   
//   -Using the code generated by TTree::MakeClass: In this case, the user
//      creates an instance of the analysis class. He has the control over
//      the event loop and he can generate an unlimited number of histograms.
//    
//   -Using the code generated by TTree::MakeSelector. Like for the code
//      generated by TTree::MakeClass, the user can do complex analysis.
//      However, he cannot control the event loop. The event loop is controlled
//      by TTree::Process called by the user. This solution is illustrated
//      by the current code. The advantage of this method is that it can be run
//      in a parallel environment using PROOF (the Parallel Root Facility).
//    
// A chain of 4 files (originally converted from PAW ntuples) is used
// to illustrate the various ways to loop on Root data sets.
// Each data set contains a Root Tree named "h42"
// The class definition in h1analysis.h has been generated automatically
// by the Root utility TTree::MakeSelector using one of the files with the
// following statement:
//       h42->MakeSelector("h1analysis");
// This produces two files: h1analysis.h and h1analysis.C (skeleton of this file)
// The h1analysis class is derived from the Root class TSelector.
//
// The following members functions are called by the TTree::Process functions.
//    Begin:       called everytime a loop on the tree starts.
//                 a convenient place to create your histograms.
//    Notify():    This function is called at the first entry of a new Tree
//                 in a chain.
//    ProcessCut:  called at the beginning of each entry to return a flag
//                 true if the entry must be analyzed.
//    ProcessFill: called in the entry loop for all entries accepted 
//                 by Select. 
//    Terminate:   called at the end of a loop on a TTree.
//                 a convenient place to draw/fit your histograms.
//
//   To use this file, try the following session
//
// Root > gROOT->Time(); //will show RT & CPU time per command
//
//==>   A-  create a TChain with the 4 H1 data files
// The chain can be created by executed the short macro h1chain.C below:
// {
//   TChain chain("h42");
//   chain.Add("$H1/dstarmb.root");  //  21330730 bytes  21920 events
//   chain.Add("$H1/dstarp1a.root"); //  71464503 bytes  73243 events
//   chain.Add("$H1/dstarp1b.root"); //  83827959 bytes  85597 events
//   chain.Add("$H1/dstarp2.root");  // 100675234 bytes 103053 events
//   //where $H1 is a system symbol pointing to the H1 data directory.
// }
//
// Root > .x h1chain.C
//
//==>   B- loop on all events
// Root > chain.Process("h1analysis.C")
//
//==>   C- same as B, but in addition fill the event list with selected entries.
// The event list is saved to a file "elist.root" by the Terminate function.
// To see the list of selected events, you can do elist->Print("all").
// The selection function has selected 7525 events out of the 283813 events
// in the chain of files. (2.65 per cent)
// Root > chain.Process("h1analysis.C","fillList")
//
//==>   D- Process only entries in the event list
// The event list is read from the file in elist.root generated by step C
// Root > chain.Process("h1analysis.C","useList")
//
//==>   E- the above steps have been executed via the interpreter.
//      You can repeat the steps B, C and D using the script compiler
//      by replacing "h1analysis.C" by "h1analysis.C+" or "h1analysis.C++"
//
// in a new session with ,eg:
//
//==>   F- Create the chain as in A, then execute
// Root > chain.Process("h1analysis.C+","useList")
//
// The commands executed with the 4 different methods B,C,D and E
// produce two canvases shown below:
//  the Dstar plot 
//  the Tau D0 plot 

#include "h1analysis.h"
#include "TH2.h"
#include "TF1.h"
#include "TStyle.h"
#include "TCanvas.h"
#include "TLine.h"
#include "TEventList.h"

const Double_t dxbin = (0.17-0.13)/40;   // Bin-width  
const Double_t sigma = 0.0012;
TEventList *elist = 0;
Bool_t useList, fillList;
TH1F *hdmd;
TH2F *h2;

//_____________________________________________________________________
Double_t fdm5(Double_t *xx, Double_t *par)
{
   Double_t x = xx[0];
   if (x <= 0.13957) return 0;
   Double_t xp3 = (x-par[3])*(x-par[3]);
   Double_t res = dxbin*(par[0]*TMath::Power(x-0.13957, par[1])    
       + par[2] / 2.5066/par[4]*TMath::Exp(-xp3/2/par[4]/par[4]));   
   return res;
}

//_____________________________________________________________________
Double_t fdm2(Double_t *xx, Double_t *par)
{
   Double_t x = xx[0];
   if (x <= 0.13957) return 0;
   Double_t xp3 = (x-0.1454)*(x-0.1454);
   Double_t res = dxbin*(par[0]*TMath::Power(x-0.13957, 0.25)    
       + par[1] / 2.5066/sigma*TMath::Exp(-xp3/2/sigma/sigma));   
   return res;
}

//_____________________________________________________________________
void h1analysis::Begin(TTree *tree)
{
// function called before starting the event loop
//  -it performs some cleanup
//  -it creates histograms
//  -it sets some initialisation for the event list
     
   //initialize the Tree branch addresses
   Init(tree);

   //print the option specified in the Process function.
   TString option = GetOption();
   printf("Starting h1analysis with process option: %sn",option.Data());
      
   //some cleanup in case this function had already been executed
   //delete any previously generated histograms or functions
   gDirectory->Delete("hdmd");
   gDirectory->Delete("h2*");
   delete gROOT->GetFunction("f5");
   delete gROOT->GetFunction("f2");
   
   //create histograms
   hdmd = new TH1F("hdmd","dm_d",40,0.13,0.17);
   h2   = new TH2F("h2","ptD0 vs dm_d",30,0.135,0.165,30,-3,6);
   
   //process cases with event list
   fillList = kFALSE;
   useList  = kFALSE;
   fChain->SetEventList(0);
   delete gDirectory->GetList()->FindObject("elist");
   // case when one creates/fills the event list
   if (option.Contains("fillList")) {
      fillList = kTRUE;
      elist = new TEventList("elist","selection from Cut",5000);
   }
   // case when one uses the event list generated in a previous call
   if (option.Contains("useList")) {
      useList  = kTRUE;
      TFile f("elist.root");
      elist = (TEventList*)f.Get("elist");
      if (elist) elist->SetDirectory(0); //otherwise the file destructor will delete elist
      fChain->SetEventList(elist);
   }
}

//_____________________________________________________________________
Bool_t h1analysis::ProcessCut(Int_t entry)
{
// Selection function to select D* and D0.
      
   //in case one event list is given in input, the selection has already been done.
   if (useList) return kTRUE;

   // Read only the necessary branches to select entries.
   // return as soon as a bad entry is detected
   b_md0_d->GetEntry(entry);   if (TMath::Abs(md0_d-1.8646) >= 0.04) return kFALSE;
   b_ptds_d->GetEntry(entry);  if (ptds_d <= 2.5) return kFALSE;
   b_etads_d->GetEntry(entry); if (TMath::Abs(etads_d) >= 1.5) return kFALSE;
   b_ik->GetEntry(entry);  ik--; //original ik used f77 convention starting at 1
   b_ipi->GetEntry(entry); ipi--;
   b_ntracks->GetEntry(entry);
   b_nhitrp->GetEntry(entry);
   if (nhitrp[ik]*nhitrp[ipi] <= 1) return kFALSE;
   b_rend->GetEntry(entry);
   b_rstart->GetEntry(entry);
   if (rend[ik] -rstart[ik]  <= 22) return kFALSE;
   if (rend[ipi]-rstart[ipi] <= 22) return kFALSE;
   b_nlhk->GetEntry(entry);         if (nlhk[ik] <= 0.1)    return kFALSE;
   b_nlhpi->GetEntry(entry);        if (nlhpi[ipi] <= 0.1)  return kFALSE;
   b_ipis->GetEntry(entry); ipis--; if (nlhpi[ipis] <= 0.1) return kFALSE;
   b_njets->GetEntry(entry);        if (njets < 1)          return kFALSE;
   
   // if option fillList, fill the event list
   if (fillList) elist->Enter(fChain->GetChainEntryNumber(entry));
   return kTRUE;
}


//_____________________________________________________________________
void h1analysis::ProcessFill(Int_t entry)
{
// function called for selected entries only

   // read branches not processed in ProcessCut
   b_dm_d->GetEntry(entry);         //read branch holding dm_d
   b_rpd0_t->GetEntry(entry);       //read branch holding rpd0_t
   b_ptd0_d->GetEntry(entry);       //read branch holding ptd0_d

   //fill some histograms
   hdmd->Fill(dm_d);
   h2->Fill(dm_d,rpd0_t/0.029979*1.8646/ptd0_d);
}

//_____________________________________________________________________
void h1analysis::Terminate()
{
// function called at the end of the event loop
   
   //create the canvas for the h1analysis fit
   gStyle->SetOptFit();
   TCanvas *c1 = new TCanvas("c1","h1analysis analysis",10,10,800,600);
   c1->SetBottomMargin(0.15);
   hdmd->GetXaxis()->SetTitle("m_{K#pi#pi} - m_{K#pi}[GeV/c^{2}]");
   hdmd->GetXaxis()->SetTitleOffset(1.4);
   
   //fit histogram hdmd with function f5 using the loglikelihood option
   TF1 *f5 = new TF1("f5",fdm5,0.139,0.17,5); 
   f5->SetParameters(1000000, .25, 2000, .1454, .001);
   hdmd->Fit("f5","lr");
   
   //create the canvas for tau d0
   gStyle->SetOptFit(0);
   gStyle->SetOptStat(1100);
   TCanvas *c2 = new TCanvas("c2","tauD0",100,100,800,600);
   c2->SetGrid();
   c2->SetBottomMargin(0.15);

   // Project slices of 2-d histogram h2 along X , then fit each slice
   // with function f2 and make a histogram for each fit parameter
   // Note that the generated histograms are added to the list of objects
   // in the current directory.
   TF1 *f2 = new TF1("f2",fdm2,0.139,0.17,2);
   f2->SetParameters(10000, 10);
   h2->FitSlicesX(f2,0,0,1,"qln");
   TH1D *h2_1 = (TH1D*)gDirectory->Get("h2_1");
   h2_1->GetXaxis()->SetTitle("#tau[ps]");
   h2_1->SetMarkerStyle(21);
   h2_1->Draw();
   c2->Update();
   TLine *line = new TLine(0,0,0,c2->GetUymax());
   line->Draw();
   
   //save the event list to a Root file if one was produced
   if (fillList) {
      TFile efile("elist.root","recreate");
      elist->Write();
   }
}