1. Using Pythia 8 on the UCD Linux server with ROOT
Pythia Mini-Session
Using Pythia 8 on the UCD Linux server with ROOT

2. Setting up: Getting code
In your home directory, create a working directory for the Pythia installation
mkdir pythia
Download Pythia from the Pythia website.
Note: Pythia tested and works.
Later version tried and had problems, stick to 8.108
Zipped Tarball: pythia8108.tgz
After unzipping and extracting tarball, should have a directory called “pythia8108”
1/13/2019
Manuel Calderón de la Barca Sánchez

3. Interlude before setup: Documentation
Documentation area:
pythia8108/htmldoc/
Web documentation:
Open the file Welcome.html in browser
PDF documentation:
pythia8100.pdf
Of intereset:
“Study output”
Pythia Classes to manipulate the generated particles, momenta, decays etc.
“Setup Run Tasks”
Setting up the collision and beam parameters
Turning on the relevant processes processes (e.g. heavy quark production)
Phase space cuts, couplings, scales
1/13/2019
Manuel Calderón de la Barca Sánchez

4. Manuel Calderón de la Barca Sánchez
Compiling Pythia
Read the README files!
Basic installation:
type ./configure
type make
The libraries are now built!
1/13/2019
Manuel Calderón de la Barca Sánchez

5. Running the first example
go to the examples directory
There are 27 programs already given as examples.
Check the README file (in the examples area)
Start with main01.cc
Check that it works:
Type: make main01
Type: ./main01.exe
1/13/2019
Manuel Calderón de la Barca Sánchez

6. Compiling: Makefile compilation
Default: main00-main27 are compiled with:
../$(LIBDIRARCH)/libpythia8.a
@mkdir -p ../$(BINDIR)
$(CXX) $(CXXFLAGS) -I../$(INCDIR) -o \
-L../$(LIBDIRARCH) -lpythia8 -llhapdfdummy
@ln -fs
Where config.mk file is:
SHELL = /bin/sh
ARCH = Linux-gcc4
MYLCGPLATFORM = slc4_ia32_gcc34
SHAREDLIBS = no
FC = gfortran
CC = gcc
FFLAGS = -O2
CFLAGS = -O2
CXXFLAGS = -O2 -ansi -pedantic -W -Wall -Wshadow
FLIBS = -lgfortran -lgfortranbegin
1/13/2019
Manuel Calderón de la Barca Sánchez

7. Manuel Calderón de la Barca Sánchez
To use ROOT: Changes I
Remove “pedantic” compilation flag in config.mk file.
Rtypes.h uses long long type, not supported by ISO C++.
Compiler needs to know ROOT includes, compiling flags, library path
Add following to Makefile
ROOTINC=($ROOTSYS)/include
ROOTCFLAGS = -pthread -m32 -I/nuclearsoft/root/include
ROOTLIBS = -L/nuclearsoft/root/lib -lCore -lCint -lRIO -lNet -lHist -lGraf -lGraf3d -lGpad -lTree -lRint -lPostscript -lMatrix -lPhysics -lMathCore -lThread -pthread -lm -ldl -rdynamic
CXXFLAGS += $(ROOTCFLAGS)
1/13/2019
Manuel Calderón de la Barca Sánchez

8. Manuel Calderón de la Barca Sánchez
To use ROOT: Changes II
Make use of main00
Makefile supports main00, but it is not given as example.
Copy main01 to main00 and work from main00
Add specific instructions in Makefile for main00
main00 : \
../$(LIBDIRARCH)/libpythia8.a
@mkdir -p ../$(BINDIR)
$(CXX) $(CXXFLAGS) -I../$(INCDIR) -o \
-L../$(LIBDIRARCH) -lpythia8 -llhapdfdummy\
$(ROOTLIBS)
@ln -fs
1/13/2019
Manuel Calderón de la Barca Sánchez

9. A closer look at the first example
main00 should now be a copy of main01
main01 did the following:
Turned on all QCD Hard processes
Sampled phase-space with pTHat > 20
Check web documentation
Phase space cuts, cuts in 2 → 2 processes
pTHatMin : The minimum invariant pT
intializes Pythia for p+p collisions at 14 TeV
creates a Pythia Histogram to save the output of the charged multiplicity
Makes a loop to generate 100 events
Inside loop:
Generates the next event
lists the first event
Loops over all particles in the event record, counts all final state particles that are charged
fills the multiplicity histogram for the event
Prints the statistics of the event (cross section, e.g.)
Prints the ascii histogram to the terminal
1/13/2019
Manuel Calderón de la Barca Sánchez

10. Modification to use ROOT histogram
Includes:
#include "TROOT.h"
#include "TFile.h"
#include "TH1.h"
Add root histogram (instead of Pythia histogram)
TH1D* multHist = new TH1D("multHist","Multiplicity",100,-0.5,99.5);
Can also change pTHatMin to 1 for MinBias
Fill histogram (instead of Pythia histogram)
multHist->Fill(nCharged);
Write output
TFile* outFile = new TFile("pythiaOutputHistosTest.root","RECREATE");
multHist->Write();
outFile->Close();
1/13/2019
Manuel Calderón de la Barca Sánchez