{
"cells": [
{
"cell_type": "markdown",
"metadata": {},
"source": [
"\n",
" ![](\"../../images/ATLASOD.gif\")
\n",
""
]
},
{
"cell_type": "markdown",
"metadata": {},
"source": [
"Searching for the Higgs boson in the H→γγ channel
\n",
"\n",
"## C++ notebook example"
]
},
{
"cell_type": "markdown",
"metadata": {},
"source": [
"**Introduction**\n",
"Let's take a current ATLAS Open Data sample and create a histogram:"
]
},
{
"cell_type": "markdown",
"metadata": {},
"source": [
"In order to activate the interactive visualisation of the histogram that is later created we can use the JSROOT magic:"
]
},
{
"cell_type": "code",
"execution_count": 1,
"metadata": {},
"outputs": [],
"source": [
"%jsroot on"
]
},
{
"cell_type": "markdown",
"metadata": {},
"source": [
"We need to include some standard C++ and ROOT libraries"
]
},
{
"cell_type": "code",
"execution_count": 2,
"metadata": {},
"outputs": [],
"source": [
"// Creates a TChain to be used by the Analysis.C class\n",
"#include \n",
"#include \n",
"#include \n",
"#include \n",
"#include \n",
"#include "
]
},
{
"cell_type": "markdown",
"metadata": {},
"source": [
"Because we would like to use more than one ROOT input file, the best option is to use a TChain object. This allows to \"chain\" several samples into a single structure that we can later loop over"
]
},
{
"cell_type": "code",
"execution_count": 3,
"metadata": {
"scrolled": true
},
"outputs": [
{
"name": "stdout",
"output_type": "stream",
"text": [
"(TString &) \"https://atlas-opendata.web.cern.ch/atlas-opendata/samples/2020/GamGam/\"[70]\n"
]
}
],
"source": [
"TString path = \"https://atlas-opendata.web.cern.ch/atlas-opendata/samples/2020/GamGam/\""
]
},
{
"cell_type": "code",
"execution_count": 4,
"metadata": {},
"outputs": [],
"source": [
"TChain* fChain = new TChain(\"mini\");\n",
"\n",
"fChain->AddFile(path+\"Data/data_A.GamGam.root\");\n",
"fChain->AddFile(path+\"Data/data_B.GamGam.root\");\n",
"fChain->AddFile(path+\"Data/data_C.GamGam.root\");\n",
"fChain->AddFile(path+\"Data/data_D.GamGam.root\");"
]
},
{
"cell_type": "markdown",
"metadata": {},
"source": [
"Now we're going to extract the photons variables"
]
},
{
"cell_type": "code",
"execution_count": 5,
"metadata": {},
"outputs": [],
"source": [
"UInt_t Photon_n = -1; //number of preselected photons\n",
"\n",
"vector *Photon_pt; //transverse momentum of the photon\n",
"vector *Photon_eta = 0; //pseudorapidity of the photon\n",
"vector *Photon_phi = 0; //azimuthal angle of the photon\n",
"vector *Photon_E = 0; //energy of the photon\n",
"vector *Photon_isTightID = 0;\n",
"\n",
"Bool_t TrigP = 0;\n",
"vector *Photon_ptcone30 = 0;\n",
"vector *Photon_etcone20 = 0;"
]
},
{
"cell_type": "markdown",
"metadata": {},
"source": [
"Here we're filling the variables defined above with the content of those inside the input ntuples"
]
},
{
"cell_type": "code",
"execution_count": 6,
"metadata": {},
"outputs": [],
"source": [
"fChain->SetBranchAddress(\"photon_pt\", &Photon_pt); \n",
"fChain->SetBranchAddress(\"photon_n\", &Photon_n); \n",
"\n",
"fChain->SetBranchAddress(\"photon_eta\", &Photon_eta);\n",
"fChain->SetBranchAddress(\"photon_phi\", &Photon_phi);\n",
"fChain->SetBranchAddress(\"photon_E\", &Photon_E);\n",
"fChain->SetBranchAddress(\"photon_isTightID\", &Photon_isTightID);\n",
"\n",
"fChain->SetBranchAddress(\"trigP\", &TrigP);\n",
"fChain->SetBranchAddress(\"photon_ptcone30\", &Photon_ptcone30);\n",
"fChain->SetBranchAddress(\"photon_etcone20\", &Photon_etcone20);"
]
},
{
"cell_type": "markdown",
"metadata": {},
"source": [
"We're creating a histogram for this example. The plan in to fill them with events."
]
},
{
"cell_type": "code",
"execution_count": 7,
"metadata": {},
"outputs": [],
"source": [
"//Invariant mass histograms definition\n",
"TH1F *h_M_Hyy = new TH1F(\"h_M_Hyy\",\"Diphoton invariant-mass ; M_{#gamma#gamma} [GeV] ; Events / bin\", 30, 105, 160);"
]
},
{
"cell_type": "markdown",
"metadata": {},
"source": [
"We are selecting below a simple look for them."
]
},
{
"cell_type": "code",
"execution_count": 8,
"metadata": {},
"outputs": [],
"source": [
"h_M_Hyy->SetMarkerSize(2.0);\n",
"h_M_Hyy->SetLineColor(kBlue);\n",
"h_M_Hyy->SetFillColor(kBlue-10);"
]
},
{
"cell_type": "markdown",
"metadata": {},
"source": [
"The Higgs boson analysis implemented here considers Higgs boson decays into a photon pair. The event selection criteria are:"
]
},
{
"cell_type": "code",
"execution_count": 9,
"metadata": {},
"outputs": [
{
"name": "stdout",
"output_type": "stream",
"text": [
"* Total number of entries to analyse: 7798424\n",
"* Analysed a total of: 7798424 in this sample.\n"
]
}
],
"source": [
"int nentries, nbytes, i;\n",
"nentries = (Int_t)fChain->GetEntries();\n",
"\n",
"std::cout << \"* Total number of entries to analyse: \" << nentries << std::endl;\n",
"\n",
"// Preselection of good photons\n",
"\n",
"for (i=0; i < nentries; i++)\n",
"{\n",
" nbytes = fChain->GetEntry(i);\n",
" \n",
" //# Cut: Diphoton trigger is satisfied\n",
" if(TrigP)\n",
" {\n",
" int goodphoton_index[5]; // give the vector a size good enough to avoid segmentation faults due to events with more than 2 photons.\n",
" int goodphoton_n = 0; // the total number of good photon\n",
" int photon_index = 0;\n",
" \n",
" for(unsigned int j=0; jat(j))\n",
" {\n",
" //# Cut: two photons with 25 GeV and excluding the transition region between the barrel and endcap calorimeters\n",
" if(Photon_pt->at(j) >25000. && TMath::Abs(Photon_eta->at(j))<2.37 && \n",
" (TMath::Abs(Photon_eta->at(j)) < 1.37 || TMath::Abs(Photon_eta->at(j)) > 1.52))\n",
" {\n",
" goodphoton_n = goodphoton_n + 1; // count\n",
" goodphoton_index[photon_index] = j;\n",
" photon_index++;\n",
" }\n",
" }\n",
" }\n",
"\n",
" //# Cut: Exactly two photons \n",
" if(goodphoton_n==2)\n",
" {\n",
" int goodphoton1_index = goodphoton_index[0];\n",
" int goodphoton2_index = goodphoton_index[1];\n",
" // isolated photons\n",
" if(((Photon_ptcone30->at(goodphoton1_index)/Photon_pt->at(goodphoton1_index)) < 0.065) && ((Photon_etcone20->at(goodphoton1_index) / Photon_pt->at(goodphoton1_index)) < 0.065 ))\n",
" {\n",
" if(((Photon_ptcone30->at(goodphoton2_index)/Photon_pt->at(goodphoton2_index)) < 0.065) && ((Photon_etcone20->at(goodphoton2_index) / Photon_pt->at(goodphoton2_index)) < 0.065 ))\n",
" {\n",
" // TLorentzVector definitions\n",
" TLorentzVector Photon_1 = TLorentzVector();\n",
" TLorentzVector Photon_2 = TLorentzVector();\n",
" \n",
" Photon_1.SetPtEtaPhiE(Photon_pt->at(goodphoton1_index), Photon_eta->at(goodphoton1_index), Photon_phi->at(goodphoton1_index),Photon_E->at(goodphoton1_index));\n",
" Photon_2.SetPtEtaPhiE(Photon_pt->at(goodphoton2_index), Photon_eta->at(goodphoton2_index), Photon_phi->at(goodphoton2_index),Photon_E->at(goodphoton2_index));\n",
" \n",
" float dPhi_yy = fabs(Photon_phi->at(goodphoton1_index) - Photon_phi->at(goodphoton2_index));\n",
" dPhi_yy = dPhi_yy < TMath::Pi() ? dPhi_yy : 2*TMath::Pi() - dPhi_yy;\n",
" float m_yy = sqrt( 2 * Photon_1.Pt() * Photon_2.Pt() * \n",
" (cosh( Photon_1.Eta() - Photon_2.Eta()) - cos(dPhi_yy)));\n",
" \n",
" //Calculation of the Invariant Mass using TLorentz vectors\n",
" TLorentzVector Photon_12 = Photon_1 + Photon_2;\n",
" float mass_inv_GeV = Photon_12.M()/1000.;\n",
" \n",
" h_M_Hyy->Fill(mass_inv_GeV);\n",
" }\n",
" }\n",
" }\n",
" } // end TrigPhoton request\n",
"}\n",
"\n",
"std::cout << \"* Analysed a total of: \" << nentries << \" in this sample.\" << std::endl;"
]
},
{
"cell_type": "markdown",
"metadata": {},
"source": [
"#### Final plot"
]
},
{
"cell_type": "code",
"execution_count": 10,
"metadata": {},
"outputs": [
{
"data": {
"text/html": [
"\n",
"\n",
"
\n",
"\n",
"\n"
],
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""
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"metadata": {},
"output_type": "display_data"
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],
"source": [
"TCanvas *cz = new TCanvas(\"cz\",\"cz\",10,10,900,600);\n",
"TText tz; tz.SetTextFont(42); tz.SetTextAlign(21);\n",
"h_M_Hyy->Draw();\n",
"cz->Draw();"
]
},
{
"cell_type": "markdown",
"metadata": {},
"source": [
"#### Log Scale"
]
},
{
"cell_type": "code",
"execution_count": 11,
"metadata": {},
"outputs": [
{
"data": {
"text/html": [
"\n",
"\n",
"
\n",
"\n",
"\n"
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""
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],
"source": [
"h_M_Hyy->Draw(\"E3\");\n",
"cz->SetLogy();\n",
"cz->Draw();"
]
},
{
"cell_type": "markdown",
"metadata": {},
"source": [
"**Done!**"
]
}
],
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"kernelspec": {
"display_name": "ROOT C++",
"language": "c++",
"name": "root"
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