//must have zee.root in the same directory
TCanvas * zeemass()                                     	  //returns the canvas which displays the histogram
{
  
  TDirectory * f =(TDirectory *)new TFile("zee.root");            //opens file zee.root
  f=(TDirectory)f->Get("STNTUPLE");                               //opens directory STNTUPLE
  TTree *h1=f->Get("h1");                                         //set h1 as a pointer to tree h1
  
  TH1F *hist =new TH1F("hist","Mass of Z boson",100,81,101);      //makes a histogram with 100 bins ranging from 81 to101
  TLeaf *lmass = h1->GetLeaf("Eemass");                           //Sets lmass as a pointer to the leaf for Eemass
  TLeaf *lcharge = h1->GetLeaf("Echarge");
  TLeaf *lnel = h1->GetLeaf("Nel");
  
  Int_t nev = lmass->GetBranch()->GetEntries();		          //# of events

  for (Int_t i=0; i<nev;i++)
    {
      lnel->GetBranch()->GetEvent(i);                             //go to the ith event
      
      if(lnel->GetValue()==2)	                                  //only events with 2 electrons
	{
      	  lcharge->GetBranch()->GetEvent(i);
	  	  	  
	  if ((lcharge->GetValue(0))==-(lcharge->GetValue(1)))
	    {
	      lmass->GetBranch()->GetEvent(i);
	      hist->Fill(lmass->GetValue(0));                     //put Eemass in the histogram
	    }
	  
	}
    }
  TCanvas *c1=new TCanvas("c1","Mass of Z bososn",700,700);       //creates a mew canvas
  hist->Draw();					                  //draw the histogram
  hist->Fit("gaus");                                              //fits a gauss curve to the histogram

  return (c1);
}