[RDF,Tutorial] Add tutorial processing NanoAOD-like file producing dimuon...

[RDF,Tutorial] Add tutorial processing NanoAOD-like file producing dimuon spectrum from Run2011A CMS OpenData

tutorials/dataframe/df102_NanoAODDimuonAnalysis.C

+/// \file
+/// \ingroup tutorial_dataframe
+/// \notebook -nodraw
+/// This tutorial illustrates how NanoAOD files can be processed with ROOT
+/// dataframes. The NanoAOD-like input file is filled with events from
+/// CMS OpenData containing muon candidates from 2011 data
+/// (DOI: 10.7483/OPENDATA.CMS.RZ34.QR6N). The script matches muon pairs
+/// and produces an histogram of the dimuon mass spectrum showing resonances
+/// up to the Z mass.
+///
+/// \macro_code
+///
+/// \date August 2018
+/// \author Stefan Wunsch
+
+#include "ROOT/RDataFrame.hxx"
+#include "ROOT/RVec.hxx"
+#include "TCanvas.h"
+#include "TH1D.h"
+#include "TLatex.h"
+#include "TLorentzVector.h"
+#include "TStyle.h"
+
+using namespace ROOT::VecOps;
+
+void DrawSpectrum(TH1D& h);
+
+void df102_NanoAODDimuonAnalysis()
+{
+   // Enable implicit multi-threading
+   ROOT::EnableImplicitMT();
+
+   // Create dataframe from NanoAOD file
+   ROOT::RDataFrame df("Events", "NanoAOD_DoubleMuon_CMS2011OpenData.root");
+
+   // Select events with more than two muons
+   auto df_filtered = df.Filter("nMuon>=2", "More than two muons");
+
+   // Find muon pair with highest pt and opposite charge
+   auto find_pair = [](const RVec<float> &pt, const RVec<int> &charge) {
+      // Get indices that sort the muon pts in descending order
+      const auto idx = Reversed(Argsort(pt));
+
+      // Find muon with second-highest pt and opposite charge
+      const auto i1 = idx[0];
+      for (size_t i = 1; i < idx.size(); i++) {
+         const auto i2 = idx[i];
+         if (charge[i1] != charge[i2]) {
+            return RVec<size_t>({i1, i2});
+         }
+      }
+
+      // Return empty selection if no candidate matches
+      return RVec<size_t>({});
+   };
+   auto df_pair = df_filtered.Define("Muon_pair", find_pair, {"Muon_pt", "Muon_charge"})
+                             .Filter("Muon_pair.size() == 2", "Found valid pair");
+
+   // Compute invariant mass of the di-muon system
+   auto compute_mass = [](RVec<float> &pt, RVec<float> &eta, RVec<float> &phi,
+                          RVec<float> &mass, RVec<size_t> &idx) {
+      // Compose four-vectors of both muons
+      TLorentzVector p1;
+      const auto i1 = idx[0];
+      p1.SetPtEtaPhiM(pt[i1], eta[i1], phi[i1], mass[i1]);
+
+      TLorentzVector p2;
+      const auto i2 = idx[1];
+      p2.SetPtEtaPhiM(pt[i2], eta[i2], phi[i2], mass[i2]);
+
+      // Add four-vectors to build di-muon system and return the invariant mass
+      return (p1 + p2).M();
+   };
+   auto df_mass = df_pair.Define("Dimuon_mass", compute_mass,
+                                 {"Muon_pt", "Muon_eta", "Muon_phi", "Muon_mass", "Muon_pair"});
+
+   // Plot histogram of di-muon mass spectrum
+   auto h = df_mass.Histo1D({"Dimuon_mass", "Dimuon_mass", 20000, 0.25, 300}, "Dimuon_mass")
+                   .GetValue();
+
+   // Draw histogram
+   DrawSpectrum(h);
+}
+
+int main()
+{
+   df102_NanoAODDimuonAnalysis();
+}
+
+void DrawSpectrum(TH1D& h)
+{
+   gStyle->SetOptStat(0);
+   gStyle->SetTextFont(42);
+   TCanvas c("c", "c", 800, 600);
+   c.SetLogx();
+   c.SetLogy();
+
+   h.SetTitle("");
+   h.GetXaxis()->SetTitle("Invariant di-muon mass (GeV)");
+   h.GetXaxis()->SetTitleSize(0.04);
+   h.GetYaxis()->SetTitle("N_{Events}");
+   h.GetYaxis()->SetTitleSize(0.04);
+   h.Draw();
+
+   TLatex label;
+   label.SetNDC(true);
+   label.DrawLatex(0.175, 0.740, "#eta");
+   label.DrawLatex(0.205, 0.785, "#rho,#omega");
+   label.DrawLatex(0.270, 0.750, "#phi");
+   label.DrawLatex(0.400, 0.800, "J/#psi");
+   label.DrawLatex(0.415, 0.680, "#psi'");
+   label.DrawLatex(0.485, 0.760, "Y(1,2,3S)");
+   label.DrawLatex(0.755, 0.620, "Z");
+
+   label.DrawLatex(0.170, 0.350, "#bf{CMS Open Data}");
+   label.DrawLatex(0.170, 0.275, "#bf{#sqrt{s} = 7 TeV}");
+   label.DrawLatex(0.170, 0.200, "#bf{L_{int} = 2.4 fb^{-1}}");
+   label.SetTextSize(0.032);
+   label.DrawLatex(0.10, 0.920, "Run2011A Double Muon Dataset (DOI: 10.7483/OPENDATA.CMS.RZ34.QR6N)");
+
+   c.SaveAs("nanoaod_dimuon_spectrum.pdf");
+}