Pythia Tutorial Program

Example of a simple program and some distributions.

Higgs program

Now look at my_higgs.f. In my_analyse it defines some objects: isolated lepton (private subroutine), missing energy (private subroutine) and jets (pycell - Pythia subroutine). The program makes some plots using paw (the tutorial.hbook file). Try to plot the invariant mass of two isolated leptons (the invariant mass of two four vectors is the mass of the sum of this vectors).

To view the histograms on d0server just do

guest@d0server:~/pedro/tutorial> setup cern

guest@d0server:~/pedro/tutorial> paw++

In the paw++ window server click in hbook and open the file tutorial.hbook. It will appear a LUN1 directory. Click on it. Several histograms numbered by 101...107 will appear. Just double click on it.

The program also print in an ask file four vectors from the objects (leptons and jets). Working with this four vectors is fast and give us more freedom to choose the tools to treat it. We built a c++ code to read this file and build root files

The read program

Copy from ~/pedro/tutorial/read to your personal directory the files: my_event.cpp, my_event.h, read.cpp, makefile and read.input. You should be able to compile in d0server (d0cms1, d0cms2 or d0cms3). my_event is a class defined in my_event.cpp with header files on my_event.h. It is a very simple class that calculate pt, invariant mass, perform some cuts, find the number of leptons of an event etc... The inputs of this program is the out put files fort.90 and fort.91 of the my_higgs.f (Understand what is being done!). So

cp ../fort.91 ntot.dat

cp ../fort.90 events.dat

To run the program we need to setup root. On d0server: > setup D0RunII p18.10.00 (This will set the fermilab version of root that is installed on this machine). Now we run it:

./read.exe This create a .root file.

Root Session

- Open the file

- Plot the Histograms

- Fit a gaussian for the invariant mass of two leptons

- Where is the Higgs?

Exercises

- Try two jets invariant mass (turn on hadronization).

- Where are the events with four leptons? Try more statistics. Force the Z to decay on muons only (see MDME(IDC,1) and dicover by yourself which are the idc that refers to Z decays).

- Plot the Higgs Invariant mass from this decay.

- 5 samples of events were generated using Pythia. Jets, isolated leptons and missing Et were find and recorded using simple routines to do a toy detector simulation (discussed in our sessions).

• ZZ -> 4 muons
• h -> ZZ -> 4 muons (Higgs Mass =190 GeV)
• h -> ZZ -> 4 muons (Higgs Mass = 500 GeV)
• h -> ZZ -> 2 muons 2 quarks (Higgs Mass = 190 GeV)
• Z -> 2 muons

-- PedroMercadante - 13 Aug 2007