void pionDecayExample()
{
   //
   // Draw diagrams of the lab and CM frames for a pion decay example.
   //
   TCanvas *c1 = new TCanvas("c1", "A canvas", 10, 10, 1000, 500);
   c1->Range(0, 0, 100, 50);
   gPad->SetFillColor(10);
   Int_t linsav = gStyle->GetLineWidth();
   gStyle->SetLineWidth(2);
   TLatex t;
   t.SetTextAlign(22);
   t.SetTextSize(0.06);
   TLine * l;
   //
   // The lab frame
   //
   t.DrawLatex(32,44,"Lab");
   Option_t atype = "|>"; // define arrow types
   Float_t asize = 0.04;
   Double_t x1 = 10.0;
   Double_t y1 = 25.0;
   Double_t x2 = 35.0;
   Double_t x3 = x2+20.0;
   Double_t y0 = y1-15.0;
   Double_t y3 = y1+15.0;
   l = new TArrow(x1, y1, x2, y1); l->Draw(); // incoming pion
   l = new TArrow(x2, y1, x2, y0); l->Draw(); // outgoing neutrino
   l = new TArrow(x2, y1, x3, y3); l->Draw(); // outgoing muon
   t.SetTextAlign(12);
   Double_t xt = x1; Double_t yt = y1+3.0;
   t.DrawLatex(xt,yt,"#pi^{+}");
   Double_t xt = x1-7.0; Double_t yt = y1-4.0;
   t.DrawLatex(xt,yt,"p_{#pi}=(#gamma m_{#pi}, #beta#gamma m_{#pi}, 0, 0)");
   Double_t xt = x2+3.0; Double_t yt = (y1+y0)/2.0;
   t.DrawLatex(xt,yt,"#nu_{#mu}");
   Double_t xt = x2; Double_t yt = y0-5.0;
   t.DrawLatex(xt,yt,"p_{#nu}=(p, 0, -p, 0)");
   Double_t xt = (x2+x3)/2.0-5.0; Double_t yt = (y1+y3)/2.0;
   t.DrawLatex(xt,yt,"#mu^{+}");
   t.SetTextAlign(32);
   Double_t xt = x3-5.0; Double_t yt = y3-1.0;
   t.DrawLatex(xt,yt,"p_{#mu}=(E_{#mu}, #beta#gamma m_{#pi}, p, 0)");
   //
   // The CM diagram
   //
   t.SetTextAlign(22);
   Double_t x0 = 80;
   t.DrawLatex(x0,44,"Center of Momentum");
   Double_t x1 = x0+15; Double_t x2 = x0-15;
   Double_t y0 = 25;
   Double_t y1 = y0+15; Double_t y2 = y0-15;
   l = new TArrow(x0, y0, x1, y1); l->Draw();
   l = new TArrow(x0, y0, x2, y2); l->Draw();
   t.SetTextAlign(12);
   Double_t xt = x0-4.0; Double_t yt = y0;
   t.DrawLatex(xt,yt,"#pi^{+}");
   Double_t xt = (x0+x1)/2.0+2.0; Double_t yt = (y0+y1)/2.0;
   t.DrawLatex(xt,yt,"#mu^{+}");
   t.SetTextAlign(32);
   Double_t xt = x1-4.0; Double_t yt = y1;
   t.DrawLatex(xt,yt,"p_{#mu}=(p, 0, -p, 0)");
   Double_t xt = (x0+x2)/2.0-2.0; Double_t yt = (y0+y2)/2.0;
   t.DrawLatex(xt,yt,"#nu_{#mu}");
   t.SetTextAlign(12);
   Double_t xt = x2+3.0; Double_t yt = y2;
   t.DrawLatex(xt,yt,"p_{#nu}=(p, 0, -p, 0)");
   
   c1->Update();
   gStyle->SetLineWidth(linsav);
}