2D Scatter Plot Only Shows Null Stats

ROOT
3

You can create, fill, and draw a 2-d histogram (TH2F). You will see its 40x40 grid of bins, drawn with the default “scatter plot” option.

  gROOT->cd(); // newly created histograms should go here
  delete gROOT->FindObjectAny("h"); // make sure it will be (re)created below
  TString varexp = "NumGammaProduced:Edep";
  TString selection = "";
#if 1 /* 0 or 1 */
  tScint->Project("h", varexp, selection);
#else /* 0 or 1 */
  tScint->Draw(varexp + " >> h", selection, "goff");
#endif /* 0 or 1 */
  TH1 *h = (TH1*)gROOT->FindObjectAny("h");
  if (h) {
    h->SetTitle("Scintillation Yield;Energy Deposited [eV];# Gamma Produced");
    h->SetStats(kTRUE);
    h->Draw();
    if (gPad) { gPad->Modified(); gPad->Update(); } // really (re)draw it
  }

You can create, fill, and draw an unbinned 2-d scatter-plot (TGraph). You will see all individual TTree’s data points.

  gROOT->cd(); // newly created histograms should go here
  TString varexp = "NumGammaProduced:Edep";
  TString selection = "";
  tScint->Draw(varexp, selection); // an unbinned 2-d scatter-plot (TGraph)
  TH2F *h = (TH2F*)gPad->GetPrimitive("htemp"); // empty, but provides axes
  if (h) {
    TDirectory *d = h->GetDirectory();
    h->SetDirectory(gROOT); // needed for "Project" and / or "Draw" below
    // h->Reset("M"); // make sure it's "clean"
#if 1 /* 0 or 1 */
    tScint->Project("+htemp", varexp, selection);
#else /* 0 or 1 */
    tScint->Draw(varexp + " >> +htemp", selection, "goff");
#endif /* 0 or 1 */
    ((TArrayF*)h)->Reset(); // "reset" histogram's bins' contents
    h->SetName("h"); // empty, except for "statistics" (and axes, of course)
    h->SetTitle("Scintillation Yield;Energy Deposited [eV];# Gamma Produced");
    h->SetStats(kTRUE);
    h->SetDirectory(d); // where it originally belonged to
    gPad->Modified(); gPad->Update(); // make sure it's really (re)drawn
    TPaveText *t = (TPaveText*)gPad->GetPrimitive("title");
    if (t) { // move the "title" to the middle
      Double_t x1 = t->GetX1NDC();
      Double_t x2 = t->GetX2NDC();
      Double_t dx = (x1 + x2) / 2.0 - 0.5;
      t->SetX1NDC(x1 - dx);
      t->SetX2NDC(x2 - dx);
      gPad->Modified(); gPad->Update(); // make sure it's really (re)drawn
    }
  }

BTW. For "e1:e2:e3" and / or "e1:e2:e3:e4" draw expressions, which produce unbinned 3-d scatter-plots (TPolyMarker3D), there is this thread and that thread.