Create TH2F gamma-gamma matrix from TTree/TChain data

ROOT
1

I’m working now on reading in data from a TTree/TChain attempting to create a 2D scatter plot for the purpose of using X/Y projections to study gamma ray concidences.

Previously, I was doing this using Fill() with a loop similar to:

[code]for (i=0; i<mult; i++) {
for (int ii=i+1; ii<mult; ii++) {
float x = gamma[i];
float y = gamma[ii];

histo->Fill(x,y);
histo->Fill(y,x);

}
}[/code]

where gamma energies are stored as floating-point numbers in an array of i values which I would store in an array using SetBranchAddress and GetEntry().

This would produce a nice symmetrical TH2 plot which we could gate on using X or Y projections to see which gamma-rays were coincident with which.

I am now faced with the problem of doing the same using TChain->Draw(), but so far I haven’t figured out how. I can do it with a single tree, but it doesn’t look I can use the same code with TChain as trying to call chain->GetEntry() throws a failure to evaluate. I need to use a chain because data is stored in multiple files containing parts of the same tree.

Is there a way that this can be done? I’ve been able to make all the other plots I want easily, but they’re simpler than this one.

2

In principle all you do with TTree can be done with chains. Can you give more details on the way GetEntry is failing ? also if you can provide a minimal example showing the problem that will help lot.

3

I’ll post the entire script, as I wrote a separate test script to experiment with how to do this before integrating back into the main script that makes all the other histos.

It looks like there is a scope issue somewhere.

[code]int GG () {

TChain tebchain(“teb”);

tebchain.Add("/mnt/bigraid/gretina-runs/atlas1593/staged/merged/Run0667/Run0667.root");
tebchain.Add("/mnt/bigraid/gretina-runs/atlas1593/staged/merged/Run0667/Run0667_1.root");
tebchain.Add("/mnt/bigraid/gretina-runs/atlas1593/staged/merged/Run0667/Run0667_2.root");
tebchain.Add("/mnt/bigraid/gretina-runs/atlas1593/staged/merged/Run0667/Run0667_3.root");
tebchain.Add("/mnt/bigraid/gretina-runs/atlas1593/staged/merged/Run0667/Run0667_4.root");

Double_t chainEntries = tebchain.GetEntries();

Float_t cc0[28] = {-1};
tebchain.SetBranchAddress(“xtals.cc”,&cc0);

/* draw and save histo we’ll be using as source /
tebchain.Draw("xtals.ccxtals.doppler>>GGsource(4096,0,4096)");

/* declare histogram we’ll use as destination */
TH2F *GG_cc0_D = new TH2F(“GG_cc0_D”, “GG, cc0, Doppler corrected”, 4096,0,4096,4096,0,4096);

/* read bin contents into an array */
Double_t binContent[4096] = {0};
Double_t ggEntries = GGsource->GetEntries();

for (int i=1; i<=4096; i++) {
binContent[i] = GGsource->GetBinContent(i);
}

for (int e=0; e<chainEntries; e++) {

int gammaMult = 0;
for (int thisreset=0; thisreset<28; thisreset++) {
  cc0[thisreset] = -1;
}

tebchain.GetEntry();

for (int m=0; m<28; m++) {
  if (cc0[m] > -1) {gammaMult++;}
}

for (int j=0; j<gammaMult; j++) {	    	    		  
  for (int jj=j+1; jj<gammaMult; jj++) {
    float ex = cc0[j];
    float ey = cc0[jj];

    GG_cc0->Fill(ex,ey);
    GG_cc0->Fill(ey,ex);
  }
}

}

new TCanvas;
GG_cc0_D->Draw();

}[/code]

And this is what shows up when running the script:

root [0] .x /mnt/bigraid/treesort/GG.c Warning in <TClass::TClass>: no dictionary for class phosWallCalc is available Warning in <TClass::TClass>: no dictionary for class calEvent is available Warning in <TClass::TClass>: no dictionary for class phosWallRaw is available Warning in <TClass::TClass>: no dictionary for class hitEvent is available Warning in <TClass::TClass>: no dictionary for class phosWallAux is available Warning in <TClass::TClass>: no dictionary for class auxHit is available Warning in <TClass::TClass>: no dictionary for class g1OUT is available Warning in <TClass::TClass>: no dictionary for class g1GammaEvent is available Warning in <TClass::TClass>: no dictionary for class g2OUT is available Warning in <TClass::TClass>: no dictionary for class g2CrystalEvent is available Warning in <TClass::TClass>: no dictionary for class g3OUT is available Warning in <TClass::TClass>: no dictionary for class g3CrystalEvent is available Warning in <TClass::TClass>: no dictionary for class g4SimOUT is available Warning in <TClass::TClass>: no dictionary for class g4Sim_abcd1234 is available Warning in <TClass::TClass>: no dictionary for class g4Sim_emittedGamma is available Warning in <TClass::TClass>: no dictionary for class Bank29 is available Warning in <TClass::TClass>: no dictionary for class cloverEvent is available Warning in <TClass::TClass>: no dictionary for class cloverPacket is available Warning in <TClass::TClass>: no dictionary for class g2IntPt is available Info in <TCanvas::MakeDefCanvas>: created default TCanvas with name c1 Error: Symbol tebchain is not defined in current scope /mnt/bigraid/treesort/GG.c:41: Error: Failed to evaluate tebchain.GetEntry *** Interpreter error recovered *** root [1]

The 1D spectrum displays properly, so I can see that it is getting the data from the chain just fine.

On a side note, is there any way to get those warnings to not display? An older script that would work with a single file containing this tree also displayed those warnings but they seem to not cause any interference with what I’m trying to do, so I don’t want to confuse users with them.

4

I have fixed a typo in my call of GetEntry() and the scope error has disappeared. Now I have an issue with the script not reading any data from the tree, though similar code worked fine for a TTree (rather than a TChain).

The script as it is is now:

[code]int GG () {

TChain tebchain(“teb”);

tebchain.Add("/mnt/bigraid/gretina-runs/atlas1593/staged/merged/Run0667/Run0667.root");
tebchain.Add("/mnt/bigraid/gretina-runs/atlas1593/staged/merged/Run0667/Run0667_1.root");
tebchain.Add("/mnt/bigraid/gretina-runs/atlas1593/staged/merged/Run0667/Run0667_2.root");
tebchain.Add("/mnt/bigraid/gretina-runs/atlas1593/staged/merged/Run0667/Run0667_3.root");
tebchain.Add("/mnt/bigraid/gretina-runs/atlas1593/staged/merged/Run0667/Run0667_4.root");

Double_t chainEntries = tebchain.GetEntries();

/* declare histogram we’ll use as destination */
TH2F *GG_cc0_D = new TH2F(“GG_cc0_D”, “GG, cc0, Doppler corrected”, 4096,0,4096,4096,0,4096);

cout << chainEntries << " entries." << endl;

Int_t ent;
cout << "Pick an entry to show: ";
cin >> ent;

/* tebchain.Show(ent); */

Float_t cc0[28] = {0}; Float_t doppler[28] = {0};

tebchain.SetBranchStatus("*",0);

tebchain.SetBranchStatus(“xtals.cc”,1);
tebchain.SetBranchStatus(“xtals.doppler”,1);

tebchain.SetBranchAddress(“xtals.cc”,&cc0);
tebchain.SetBranchAddress(“xtals.doppler”,&doppler);

for (int e=0; e<chainEntries; e++) {

for (int thisreset=0; thisreset<28; thisreset++) {
  cc0[thisreset] = 0; doppler[thisreset] = 0;      
} /* resets done */

int gammaMult = 0;

/* Int_t entryBytes = */ tebchain.GetEntry(e,0);

if (e == ent) {tebchain.Show(e);}

for (int m=0; m<28; m++) {
  if (cc0[m] != 0) {gammaMult++;}
}

if (gammaMult > 0) {
  cout << "Mult: " << gammaMult << endl;
}

for (int j=0; j<gammaMult; j++) {
  for (int jj=j+1; jj<gammaMult; jj++) {
    float ex = cc0[j];
    float ey = cc0[jj];

    GG_cc0_D->Fill(ex,ey);
    GG_cc0_D->Fill(ey,ex);
  }
}

}

new TCanvas;
GG_cc0_D->Draw();
}[/code]

And this is the output; Notice that the ‘Mult:’ display never shows, so not a single event read in properly. Yet the event randomly chosen to display on the screen does show the desired data:

Warning in <TClass::TClass>: no dictionary for class phosWallCalc is available Warning in <TClass::TClass>: no dictionary for class calEvent is available Warning in <TClass::TClass>: no dictionary for class phosWallRaw is available Warning in <TClass::TClass>: no dictionary for class hitEvent is available Warning in <TClass::TClass>: no dictionary for class phosWallAux is available Warning in <TClass::TClass>: no dictionary for class auxHit is available Warning in <TClass::TClass>: no dictionary for class g1OUT is available Warning in <TClass::TClass>: no dictionary for class g1GammaEvent is available Warning in <TClass::TClass>: no dictionary for class g2OUT is available Warning in <TClass::TClass>: no dictionary for class g2CrystalEvent is available Warning in <TClass::TClass>: no dictionary for class g3OUT is available Warning in <TClass::TClass>: no dictionary for class g3CrystalEvent is available Warning in <TClass::TClass>: no dictionary for class g4SimOUT is available Warning in <TClass::TClass>: no dictionary for class g4Sim_abcd1234 is available Warning in <TClass::TClass>: no dictionary for class g4Sim_emittedGamma is available Warning in <TClass::TClass>: no dictionary for class Bank29 is available Warning in <TClass::TClass>: no dictionary for class cloverEvent is available Warning in <TClass::TClass>: no dictionary for class cloverPacket is available Warning in <TClass::TClass>: no dictionary for class g2IntPt is available 6.97731e+06 entries. Pick an entry to show: 43746 ======> EVENT:43746 g2 = (g2OUT*)0x1470150 xtals = (vector<g2CrystalEvent>*)0x1470190 xtals.cc = 1003.247864 xtals.doppler = 1.034173

Is there a difference in how SetBranchAddress and SetBranchStatus work in TChain vs. TTree? Because the multiplicity never goes above 0, the matrix never fills.

5

I think, the best for you would be to try an “analysis skeleton”. See, for example, links in: How are multiple TTree->Draw()s done?
Note: you need to generate the “analysis skeleton” for your TChain, not for your single TTrree.