Generating events (standalone)

(standalone)

In stage 1 we have created the executable and the 2 files that contain information on the integration step. The executable takes a input the file input.dat and produces the ascii files <>.events that contain for each event:

• the 4-momenta of the incoming partons
• the 4-momenta of the outgoing top quarks and the hard gluon
• the event weight

As we defined in step 1 the executable produces ttbar-events using CTEQ5M1 as input PDF. Below we explain how to obtain these <>.event-files. To produce these events, you can use use the script:

ShipOff_MCatNLO_Rome_MatrixElements.py

In the script there are two directories you should set.

base_dir = "/user/ivov/Rome/BasicInfoCTEQ5M1/"

MatrixElement_dir = "/data/atlas/users/ivov/scratch/MatrixElement/"

And two variables to set:

Nevents = 100

Njobs = 1

The first directory has a tar file(the executable, CTEQ5M1 pdf and some files with integration constants from MCatNLO), the script to start in and a basic input file (check bullet 1) on what files it should contain and download them from here) The second directory is the output directory where the <>.event-files will be stored. With these values, the script starts 1 job that produces 100 events

1) base_dir: Create a directory with the executable and the default input parameter files: BasicInfoCTEQ5M1 This should contain the files:

• TTbar.tgz -- The tarred and zipped MCatNLO executable
• RunForestRun.py -- The script to untar the executable and start it
• inputs.BASIC -- The BASIC input file for the executable

If you look in the inputs.BASIC file you see that there are three variables that will be set by the run script for each run separately: Name output_file, Random number seed and Number of events to be produced.

2) Start the scripts: ./ShipOff_MCatNLO_Rome_MatrixElements.py

   The script will:

a) create a directory called Job1 in the current directory, b) copy all files there from the base_dir c) modify the BASIC input files to create one for this specific job c) untar the tar ball and run the executable it using the input set defined at c) d) copy the .event files to the MatrixElement_dir e) remove the Job1 directory

For now I have commented out the last step to make sure you can see what is going on. To remove the directory (otherwise you'll have to do it each time you start with run 1), simply uncomment the line

1. CleanUp(i_job) in the Main program.

3) Look at the output:

In Matrix_Element_Dir/InputAndLogfiles we now have the input-file (input_file_Job1) and logfile (log_file_Job1) for this job. In Matrix_Element_Dir we now have the file TTbarProd_1.events. This last file contains (after a header) the 4-momenta of the incoming partons and the outgoing top-quarks and hard gluon. It also produced an event-weight. Note that in our case only 13% has a gluon with a non-zero 4-momentum.