MG5+Delphes Tutorial - Bologna June 2016

Pre-requisites

To successfully build Delphes the following prerequisite packages should be installed:

• gcc/tcl:

For linux users gcc/tcl should be already installed. For Mac users you should install XCode.

• ROOT:

can be downloaded from ​https://root.cern.ch/downloading-root Go on latest release, and download a version under "Binary distributions".

Once it is installed, type:

source [path_to_installation]/root/bin/thisroot.sh

Then simply type in a terminal:

echo $ROOTSYS

If a path is shown then root is properly installed.

MadGraph5/MadEvent basic tutorial (@Leading Order)

In this part you are going to learn how to generate pardon-level and showered events with MadGraph5 (interfaced with Pythia6).

0) Create a new directory:

mkdir DelphesTutorial
cd DelphesTutorial

1) Download and install MG5 by typing in a terminal:

wget https://launchpad.net/mg5amcnlo/2.0/2.4.0/+download/MG5_aMC_v2.4.0.tar.gz
tar xzvf MG5_aMC_v2.4.0.tar.gz

2) Launch MG5:

cd MG5_aMC_v2_4_0
./bin/mg5_aMC

3) Install Pythia6 and MadAnalysis:

install pythia-pgs
install MadAnalysis

4) Generate a LO Drell-Yan process:

generate p p > e+ e-
display diagrams

5) Generate a LO Higgs process:

generate p p > h > e+ e- mu+ mu-

The diagram generation fails ... do you understand why? Type instead:

import model heft
generate p p > h > e+ e- mu+ mu-
display diagrams

This generates also diagrams containing photon internal lines. To veto that diagram type the following:

generate p p > h > e+ e- mu+ mu-  / a
display diagrams

6) Let's generate some events

output pp_h_eemm
launch pp_h_eemm

You will be prompted with a screen asking questions ... Type "ENTER". Another screen comes and asks you if you want to edit a bunch of configuration cards:

• "param_card.dat" is where the parameters of the model are stored (masses, couplings)
• "run_card.dat" is where the parameters of run are defined (ecm, number of events,

generation level cuts ..)

• "pythia_card.dat" is where parameters of the shower are defined

Open "param_card.dat" and "run_card.dat" by typing respectively "1" and "2"and have a look at them, but do not modify them for now. The editor is "vi", so to quit type ":q". Type ENTER to launch the parton-level generation.

7) When it's done, you should be prompted with a web browser. If not quit MG5 by typing "exit", and open the html file that was created and the end of the run with your web browser:

firefox [MG5DIR]/pp_h_eemm/Events/index.html

Click on "Results and Event Database" and then on "LHE plots". Have a look at the automatically generated parton-level plots. Explain the Ecm plot (this is the total invariant mass of the system, i.e of the four final state leptons). 8) Enter in MG5 again, and type:

./bin/mg5_aMC
import model heft

generate p p > h , h > e+ e- mu+ mu- / a
display diagrams

Then:

output pp_h_eemm_res
launch pp_h_eemm_res

Note the different syntax. This time, when you will be prompted with the screen asking questions ... Type "1". This will activate parton and hadronization with Pythia6, and then type ENTER. When the generation is done, have a look again at the parton-level plots.

7) Generate a new set of events, this time setting in the param_card mH = 750 GeV. !! Note that since we are keeping the higgs width value corresponding to mH = 125 GeV, this won't be a proper SM higgs with mH = 750 GeV !!

For this we don't need to re-generate the diagrams, we can simply type "launch" and edit the param_card by changing the higgs mass when prompted. If everything worked smoothly you should have two event samples with 10k events each. Events are stored in [MG5DIR]/pp_h_eemm_res/Events/run_01(02)

Now to quit MG5, type "exit". In each run sub-directory, only two files are interesting for us:

• "unweighted_events.lhe" contains hard-interaction events only, pre-hadronization and PS,

it is human readable, in so-called Les-Houches Event format (in short LHE)

• "tag_1_pythia_events.hep" contains showered and hadronized events, it is the event file

that we are going to give as input to the Delphes simulation.

This ends the very basic introduction to MG5. For an extensive list of tutorials, lectures about this tool (including matching, NLO generation, etc..) , have a look at the MadGraph School 2015 page:

​http://www.physics.sjtu.edu.cn/madgraphschool/

Delphes Tutorial

Part I - Getting Started

0) Go back to the DelphesTutorial directory

1) Get Delphes:

git clone https://github.com/delphes/delphes.git
cd delphes

or, if you don't have "git" installed, simply type:

wget http://cp3.irmp.ucl.ac.be/downloads/Delphes-3.3.2.tar.gz
tar -zxf Delphes-3.3.2.tar.gz
mv Delphes-3.3.2 delphes
cd delphes

2) Install it:

./configure
make -j 4

3) Unzip the event files previously generated with MG5, and move them in your delphes directory

gunzip ../MG5_aMC_v2_4_0/pp_h_eemm_res/Events/run_01/tag_1_pythia_events.hep.gz
gunzip ../MG5_aMC_v2_4_0/pp_h_eemm_res/Events/run_02/tag_1_pythia_events.hep.gz

mkdir -p input
mv ../MG5_aMC_v2_4_0/pp_h_eemm_res/Events/run_01/tag_1_pythia_events.hep input/pp_h_eemm_m125.hep
mv ../MG5_aMC_v2_4_0/pp_h_eemm_res/Events/run_02/tag_1_pythia_events.hep input/pp_h_eemm_m750.hep

4) Finally, let's run Delphes. If the compilation went right, you should have three executables:

• DelphesLHEF -> should not be used
• DelphesHepMC -> to be used on HepMC input format (*.hepmc)
• DelphesSTDHEP -> to be used on STDHEP input format (*.hep)

Type for instructions (note that output file comes before input file):

./DelphesSTDHEP

To run on our your input file, type:

./DelphesSTDHEP cards/delphes_card_CMS.tcl delphes_output_m125.root input/pp_h_eemm_m125.hep

5) Open freshly produced Delphes output with ROOT, and explore it.

root -l delphes_output_m125.root
TBrowser t;

In the browser, double click on the "delphes_output_m125.root", and then on the "Delphes" tree. Play around by double clicking on the various branches/observables.

You can then play plot important observable with a simple selection with the following syntax:

Delphes->Draw("Muon.PT", "Muon.PT > 20");
Delphes->Draw("Electron.PT", "Electron.PT > 20");

• Note 1: Delphes - tree name, it can be learnt e.g. from TBrowser
• Note 2: Muon/Electron - branch name; PT - variable (leaf) of this branch

  Delphes->Draw("Muon.Eta", "Muon.PT > 20");
  Delphes->Draw("Electron.Eta", "Electron.PT > 20");
  Delphes->Draw("Jet_size","Electron_size > 1 && Muon_size > 1");
  

Objects are already ordered in PT, you can then plot leading ele/mu in this way:

Delphes->Draw("Muon[0].PT", "Muon.PT > 20");
Delphes->Draw("Electron[0].PT", "Electron.PT > 20");

For more information on ROOT trees:

​http://cp3.irmp.ucl.ac.be/downloads/RootTreeDescription.html

Part II - Run a macro-based analysis on Delphes output

1) The macro examples/Example3.C produces resolution plots comparing reconstructed vs MC truth quantities. Run it on the delphes output:

root -b -q examples/Example3.C'("delphes_output_m125.root")'

It produces a bunch of plots in "png" format. Open them with your favourite image viewer:

open *.png

or

eog *.png

Understand:

• Why is the eta resolution plot for electron and muons different compared to photons?
• Where do photons come from?
• Why is the jet resolution plot shifted?

2) Let's now run a real event selection, and plot some interesting quantities. We select events with:

• >= 2 opposite sign isolated electrons , pT > 10 GeV, |eta| < 2.5
• >= 2 opposite sign isolated muons , pT > 10 GeV, |eta| < 2.5

Construct 3 invariant masses and fill them in histograms:

• min( m(e+ e-), m(mu+ mu-) )
• max( m(e+ e-), m(mu+ mu-) )
• m (e+ e- mu+ mu-)

Download the "HZZ.C" macro and save in the "examples" directory. Then open it with your favorite text editor, and make sure you understand what it does. Then run it:

root -b -q  examples/HZZ.C'("delphes_output_m125.root")'; 

Some plots are produced. Open the produced png file.

• Explain the left plot.
• Appreciate the effect of detector resolution by comparing the gen and reco histograms

Now redo this analysis, but this time using the mH = 750 GeV input file. Do not edit directly the HZZ.C file, make a copy of it and edit the copy rather.

• Spot and explain the differences with the mH = 125 GeV case.