ttbar+gamma MadGraph Generation

Introduction/Theory:

As preparation for the next LHC run of 13TeV is required to generate some simulations for ttbar+gamma events, the first step is to generate the parton level events, for this it's used MadGraph.

Analysis Description:

To use MG is required to define some series of cards, this cards will contain the information related with the kinematics and decays of the particles in the generation

Electron and Muon Cuts:

• Number of electrons >= 1
• Electron Pt > 25 GeV
• Electron eta < 2.1

Photon Cuts:

• Number of Photons >= 1
• Photon Pt > 25 GeV
• Photon eta < 2.4

b and light quarks Cuts:

• b,q,g Pt > 30 GeV
• b,q,g eta < 2.5

Isolation Cuts:

• DeltaR(lepton,photon) > 0.3
• DeltaR(b-q-g,photon) > 0.3

Prerequisites

* Setup ROOT and create a scratch area for PROOF*:

* Copy to your area and modify according to your needs the ROOT setup files:

cp ~yumiceva/RooAlias.C ~/.
cp ~yumiceva/RooCMS.C ~/.
cp ~yumiceva/RooLogon.C ~/.
cp ~yumiceva/.rootrc ~/.

* Edit rootrc file to point the PROOF sandbox to your scratch area. Change the line:

Proof.Sandbox: /uscmst1b_scratch/lpc1/cmsroc/yumiceva/proof

CMSSW

cmsrel CMSSW_5_3_3          (If the work is done in LS6 see the Computational section of this twiki)
cd CMSSW_5_3_3/src
cmsenv

Install MadGraph

wget http://madgraph.hep.uiuc.edu/Downloads/MG5_aMC_v2.5.5.tar.gz
tar -xf MG5_aMC_v2.5.5.tar.gz
cd MG5_aMC_v2.5.5.tar.gz

Now to run the MG environment use the executable

./bin/mg5_aMC 

Before running make the cms environment ready

cmsrel CMSSW_5_3_3
cd CMSSW_5_3_3/src
cmsenv

Install ExRootAnalysis

cd CMSSW_5_3_3/src          (or the desired release)
wget http://madgraph.hep.uiuc.edu/Downloads/ExRootAnalysis/ExRootAnalysis_V1.0.10.tar.gz (consult the latest version from the madgraph website according to the need. This version may not work with the current MG version)
tar zxvf ExRootAnalysis_V1.0.10.tar.gz
cd ExRootAnalysis/
make

Analysis Code (Generate Events)

• proc_card_mg5.dat contains the information of what particles are involved in the event, also can be specified how they decay
• run_card.dat contains the information of the parameters of the run like the number of events, the energy of the center of mass, PDF choices, etc.
• param_card contains the information of the parameters of the particles in the event, like mass, coupling strength, etc.
• to run a process it's required to go to MG directory (e.g.):

cd ~
cd MG5_aMC_v2_1_1
./bin/mg5_aMC proc_card_mg5.dat 

• This will create a new directory inside the MG directory, in this one will be all the required information for the generation of the events (e.g. directory called TTGamma)
• Go to the Cards directory inside the created directory and substitute there the run_card and the param_card (this step can be done also in the generation)
• To generate events, go inside the new directory and run the command:

cd ~
cd MG5_aMC_v2_1_1/TTGamma
./bin/generate_events 

• At the moment of the generation the user can choose the path for the run_card and the param_card if it wasn't done the substitution of the same inside the Card directory
• After the generation inside the directory Events will be all the files related with the event, in particular the .lhe files
• In the directory SubProcesses will be the Feynman diagrams of every sub-process of the event generated

Analyze the LHE files

Convert to root files

• To Analyze the .lhe files in a easy way, it can be used the ExRootAnalysis tool to convert the same to .root files
• To convert run:

~/(PATH)/ExRootAnalysis/ExRootLHEFConverter name_of_file.lhe new_name.root

• The files 8TeV.root and 13TeV.root contains the information of the event generation for those energies

Analyze the root files

• To Analyze the root files the code created it can be used a code develop by Dr. Francisco Yumiceva that uses pyROOT that loop over the events in the LHEF tree and fill histograms with the desired criteria:

cd CMSSW_5_3_3/src          (or your prefered release)
git init
git clone git@github.com:yumiceva/FXYExRoot.git
cd FXYExRoot
git checkout V00-00-00

• To produce plots:

cd FXYExRoot
./GenAnalysis.py -b -q
./GenAnalysis.py -b -q -s "13TeV"

• This will produce as output a root file name it results_gen_name-of-sample.root (see attached files). This file will contain all the plots related with the generated events
• The last version of GenAnalysis.py (contains the cuts) can be found in the attached files
• Important information that can be obtained after this step are the Mean and RMS values for any physical quantities in the generation (see Tables.pdf)

8TeV-13TeV Comparisson plots:

• To compare the results of two different events generation, run the commands:

cd CMSSW_5_3_3/src          (or prefered release)
git init usercode
cd usercode
git config core.sparsecheckout true
echo "cuy" > .git/info/sparse-checkout
git remote add fxy https://github.com/yumiceva/usercode.git
git pull fxy master
git fetch fxy
git checkout V10-00-01
cd cuy
scram b
rehash
cd $CMSSW_BASE/src/FXYExRoot
cuy.py -q -b -x compare.xml -f "CMS Comparisson Plots" -o plots/ -p "pdf"

• The result will be a file called cuy.root that contains the plots, and the creation of pdf files for every plot inside the Plots directory
• The files cuy.py and compare.xml can be found in the attached files
• To collect all the plots in a single pdf file, a program like Acrobat Professional can be used (see Plots-No-Cuts.pdf in the attached files)
• The file GenAnalysis can be modified to apply the desired cuts to produced new plots with the cuts (see attached files)
• Both plots, with and without cuts can be compare.