Tools for LHC
MadGraph/MadEvent
Ian-Woo Kim, Ji-Hun Kim
Seoul National University
SNU, Mar 31, 2007
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Introduction
We are facing with the exciting era with a great machine!
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Building under ground. 27 km, pp collider
√
s = 14TeV
4 Detectors : ATLAS, CMS, LHCb, ALICE
L = 10 − 100 fb−1 /yr
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We want to see a new physics from a “hard” scattering.
But the real life is not so simple.
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What is really happening is ...
We have to simulate it.
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Understanding the detector structure:
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ATLAS ( A Toroidal LHC AppratuS )
CMS (The Compact Muon Solenoid )
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Particle signatures left in the detector components
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Finally, we identify the following objects.
I
I
I
I
Photons : detected as energy in the ECAL, with no high PT
track and little energy in the HCAL
Electrons : detected as energy in the ECAL, with high PT
track and little energy in the HCAL
Muons :little energy in the calorimeters, with a high PT
track, travel to the muon detector system.
Taus : Hadronic decay to
F
F
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1 charged π ± or 1 charged π ± and 2 π 0 → “1-prong” tau single
charged track, leaves energy in HCAL, very narrow cone.
(2 π + and 1 π − ) or (1 π + and 2 π − ) → “3-prong” tau 3 tracks, a very
narrow jet with invariant mass ≤ 2 GeV.
Jets −→ next page.
Missing Transverse Energy : Summing all the transverse
energy deposited in calorimeters and the transverse momenta
of all muons
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I
Jets: Groups of particles (tracks and energy
bumps in calorimeters) that fit inside a cone in φ
and η space. (Cone algorithm needed. )
jets closely related to kinematics of partons in hard
process.
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b-tagging
Particles of a life-time τ ∼ 10−12 s, such as B 0,± may travel a
distinguishable distance cτ ∼ 100µm. −→ displaced secondary vertex
and nonzero impact parameter.
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MadGraph/MadEvent/PYTHIA/PGS
MadGraph : Feynman diagram generator
MadEvent : Event generator for hard process ( parton level
PYTHIA : Hadronization event generator ( it has more functionalities)
PGS : Pretty Good (Detector) simulator
A new model can be easily implemented in MadGraph : MSSM,
2HDM, etc → unified framework for various models.
parameter input must be set by another program. For SUSY, for
example, SoftSUSY, SUSY-HIT ( SDECAY,HDECAY)
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My system
Intel core 2-duo (Merom) T7200 2.0 GHz Memory 2G
Scientific Linux v4.4
SUSY spectrum and Decay rate calculator : SUSY-HIT
MadGraph/MadEvent/PYTHIA/PGS
Analysis tool : ROOT
lhco-to-root file converter: ExRootAnalysis (→ provide HEP
definition for ROOT)
LHC Inverse analysis tool : MARMOSET
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Web interface of MadGraph/MadEvent
It has a web interface at http://madgraph.hep.uiuc.edu
Need an id/password.
It has a summary webpage for each process.
MadEvent is provided as a source code which can be compiled in
user’s computer.
To run MadEvent+PYTHIA+PGS on the website (cluster), we must
have more previlaged id/password. → impossible to use it.
But it gives us a simple analysis tool.
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Installation
Install Scientific Linux v4.4 : http://www.scientificlinux.org
Install ROOT : http://root.cern.ch → download v5.14, compile
or directly install binaries. Make sure you set environment variables
correctly in .bashrc or .profile
Install MadGraph/MadEvent/PYTHIA/PGS
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From MadGraph webpage, download MadGraph V4, PYTHIA and PGS
package. PYTHIA and PGS are optimized for MadGraph/MadEvent.
Note that all the packages must be installed in the directory
MG_ME_v4.1.19
Install ExRootAnalysis : download from MadGraph webpage.
ExRootLHCOlympicsConverter will convert .lhco file to .root file.
(.lhco = LHC Olympics format )
Install SUSY-HIT : They can be installed seperately. The output
must be SLHA (SUSY Les Houches Accord) format which will be
used for the param_card.dat file for MadGraph.
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Running MadGraph/MadEvent/PYTHIA/PGS
You can set your own model in MadGraph. Here I will only focus on
SM and MSSM.
copy Template with your own directory name( e.g. MyTestDir )
Prepare for proc_card.dat and param_card.dat.
For SM, param_card.dat needs not be changed from Template.
for MSSM param_card.dat is just SLHA format. Note that
SoftSUSY generate only spectrum part of SLHA. We need decay rate
input. (Using SUSY-HIT)
newprocess : generate Feynman diagrams. build up numerical
analysis codes for each process. You can see such processes in
index.html
generate_events : generate parton-level events. Output files are in
the directory Events in .lhe.gz format. If PYTHIA/PGS are installed,
then it automatically run them.
cards
MadGraph
→
Ian-Woo Kim (SNU)
library
MadEvent
→
.lhe.gz
Tools for LHC
PYTHIA/PGS
→
.lhco
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LHC Olympics format
At collider, we can only identify the following elements for a given
event.
-
A high energy jet (b-tagging is possible)
an electron e ±
a muon µ±
a photon
Missing transverse momentum
LHC olympics format contains such identification.
# typ eta phi pt jmass ntrk btag had/em dummy dummy
# is increasing simply in a given event. Next event starts with 0.
Type :
0 = photon
1 = electron
2 = muon
3 = hadronically-decaying tau
4 = jet
6 = missing transverse energy
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LHC Olympics format
eta = pseudorapidity, phi = azimuthal angle, pt = transverse
momentum
jmass = invariant mass
ntrk = number of track
btag = b-tagging
had/em = ratio of hadronic vs EM energy in the calorimeter
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#
0
1
2
3
4
5
6
7
0
1
2
0
1
2
0
1
2
0
1
2
3
4
typ
2
4
4
4
4
4
6
1
6
1
6
4
6
4
4
4
4
eta
1
-0.629
0.208
2.610
0.960
-0.406
-2.456
0.000
2
1.683
0.000
3
-1.634
0.000
4
1.052
0.000
5
1.903
2.428
1.020
3.515
phi
2
4.513
5.953
1.793
0.523
3.685
1.476
3.362
1
2.868
5.774
1
5.182
2.111
0
2.529
5.918
0
4.242
5.696
2.842
4.131
Ian-Woo Kim (SNU)
pt
jmas
ntrk
btag
had/em
dum1
dum2
23.54
165.26
55.56
88.96
173.10
51.38
53.11
0.11
9.24
4.93
12.02
28.34
4.75
0.00
1.0
5.0
7.0
5.0
22.0
7.0
0.0
5.0
0.0
0.0
0.0
1.0
0.0
0.0
0.10
2.63
2.66
1.48
1.44
3.54
0.00
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
40.96
48.36
0.00
0.00
-1.0
0.0
0.0
0.0
0.01
0.00
0.0
0.0
0.0
0.0
36.88
36.23
0.00
0.00
-1.0
0.0
0.0
0.0
0.00
0.00
0.0
0.0
0.0
0.0
26.70
33.03
0.00
0.00
1.0
0.0
0.0
0.0
0.01
0.00
0.0
0.0
0.0
0.0
48.42
78.36
41.95
17.28
6.39
5.64
5.32
0.51
16.0
16.0
6.0
16.0
0.0
0.0
0.0
0.0
0.41
2.04
6.08
2.33
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
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ExRootAnalysis
ExRootAnalysis for interpreting .lhco format.
run ExRootLHCOlympicsConverter, then obtain .root format file.
.root is a snapshot of ROOT object instances.
an object LHCO which is an instance of TTree class.
To browse LHCO in ROOT,
gSystem->Load("lib/libExRootAnalysis.so");
TFile::Open("pgs_events.root");
LHCO->StartViewer();
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ExRootAnalysis
LHCO contains several branches: Event, Photon, Electron, Muon,
Tau, Jet, MissingET
They are TRootEvent, TRootPhoton, TRootElectron, TRootMuon,
TRootTau, TRootJet, TRootMissingET class objects, respectively.
Each object has data defined in
ExRootAnalysis/doc/RootTreeDescription.html
Using TTreeViewer, one can easily draw a histogram by drag and
dropping.
Use Draw with fields, cut and option, you can simply make a
histogram as you want.
We made a simple script drawing histogram w.r.t. the invariant mass
of several objects. The script in ROOT is written in C++. It can be
run on the command line, or as a batch procedure.
For detail of analysis, refer to ROOT User’s guide.
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Input files for MadGraph
Now, we know how to deal with output fils, let’s understand the input
files for MadGraph.
Every input file in Cards.
proc_card.dat specify the model and process we analyze.
To change models, just change the line in
# Begin MODEL
sm
# End
MODEL
# This is TAG. Do not modify this line
# This is TAG. Do not modify this line
→ change sm to mssm, then we can analyze MSSM.
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To specify processes, modify this
# Begin PROCESS # This is TAG. Do not modify this line
pp>e-ve~
QCD=99
QED=2
end_coup
@0
#
#
#
#
First Process
Max QCD couplings
Max QED couplings
End the couplings input
pp>e-ve~j @1
QCD=99
QED=2
end_coup
#
#
#
#
Second Process
Max QCD couplings
Max QED couplings
End the couplings input
pp>tt~
QCD=99
end_coup
# Third Process
# Max QCD couplings
# End the couplings input
@2
done
# End PROCESS
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# this tells MG there are no more procs
# This is TAG. Do not modify this line
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For model description, we can refer to
MG_ME_V4.1.19/Models/(model name)
particles.dat contains the particle information. For SM, particle
names are
d, d˜
s, s˜
b, b˜
e-, e+
mu-,mu+
ta-,ta+
g
a
h
d-quark
s-quark
b-quark
electron
muon
tau
gluon
photon
higgs
u,
c,
t,
ve,
vm,
vt,
u˜
c˜
t˜
ve˜
vm˜
vt˜
z
W-,W+
u-quark
c-quark
t-quark
e-neutrino
µ-neutrino
τ -neutrino
Z-boson
W-boson
interaction.dat contains the interactions.
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Let us build our new model. Consider 4th generation lepton e 0 whose
charge is the same as the electron and vector-like. Assume it has a
flavor-changing neutral current coupled to the electron mediated by Z
boson.
First, the template directory usrmod must be copied with an
appropriate name, say Myeprime.
Change particle.dat. Add new particle content.
#MODEL EXTENSION
epep+
# END
F
S
EPMASS EPWID
S
ep
2500022
Change interactions.dat. Add new interactions.
#
USRVertex
ep- ep- a GAL
ep- ep- z GEPEPZ
ep- e- z GEPEZ
e- ep- z GEPEZ
QED
QED
QED
QED
Set new parameter variables in VariableName.dat.
Run ConversionScript.pl. This generates couplings.f
Enter the expression for couplings in terms of parameters.
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Now, decide what processes will be event-generated. proc_card.dat
sets the model and the processes.
initial > intermediate > final
Here, we want to generate new physics signal only.
# Begin PROCESS # This is TAG. Do not modify this line
#e-e+ > ep- ep+ > e-e+e-e+
# First Process
u u~ > ep+ > z e+ e- @1
QCD=99
# Max QCD couplings
QED=9
# Max QED couplings
end_coup
# End the couplings input
u u~ > ep- > z e+ e- @2
QCD=99
# Max QCD couplings
QED=9
# Max QED couplings
end_coup
# End the couplings input
u u~ > ep- ep+ > z z e+ e- @3
QCD=99
# Max QCD couplings
QED=9
# Max QED couplings
end_coup
# End the couplings input
done
# this tells MG there are no more procs
# End PROCESS # This is TAG. Do not modify this line
#*********************************************************************
# Model information
*
#*********************************************************************
# Begin MODEL # This is TAG. Do not modify this line
myeprime
# End
MODEL # This is TAG. Do not modify this line
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Run newprocess. Then, new param_card.dat is generated. Enter
proper parameter values in param_card.dat.
Run generate_events.
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param_card.dat : Les Houches Accord format.
This must contain mass spectrum and decay rates.
For MSSM, we already have MadGraph model definition in
Models/mssm. param_card.dat is of SUSY Les Houches Accord
format. We can obtain such parameters from GUT scale SUSY
breaking model definition using SUSY-HIT (
SUspect-SdecaY-Hdecay-InTerface )
SUSY-HIT has inputs from susyhit.in and suspect2.in
It generates SLHA format file susyhit_slha.out It can directly be
renamed to param_card.dat
MadGraph has another input cards for Pythia and PGS.
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After newprocess, MadGraph generates the info webpage.
index.html
For collective particle like protons and jets, in and out particle is one
of the components, so a process is divided into several subprocesses.
MadGraph generates a MadEvent code madevent.tar.gz
After running generate_events, at the homepage, we can access
data : Parton-level( LHE format ), Hadron-level(Pythia, STDHEP
format), Recognized Objects( LHCO format ).
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ENJOY YOUR MONTE CARLO SIMULATION!
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