Generating Higgs To 4 Muons at NIKHEF

An exercise to simulated Higgs production events at the LHC, where the Higgs boson decays into 2 Z bosons that each decay into 2 muons.

$H\rightarrow ZZ^{*}\rightarrow \mu ^{+}\mu ^{-}\mu ^{+}\mu ^{-}$

The exercise is ment as a starting point for the 'monkey-see monkey-do' technique. In this example we will use AtlFast for the detector simulation and reconstruction. We will produce an AOD that contains the MC truth and reconstructed AtlFast objects. Since the AOD is in pool format we will also transfor the AOD into an Ntuple that allows a simple analysis program to be constructed in Root.

Note: We assume you have the CMT and Athena set-up at NIKHEF in ordnung Starting with CMT and Athena at NIKHEF

0. Setting up the ATLAS environment at NIKHEF

First set up the ATLAS environment at NIKHEF. Follow the instructions on: ATLAS setup at NIKHEF.

1. producing 10 events

a) Go to your favorite area and create a running directory

At NIKHEF a logical place would be your project disk:

cd /project/atlas/users/<your_login_name>

mkdir MyGeneration

b) Create your joboptions file

Each athena job requires a joboptions file as input. Here we will create a joboption file that will:

• Define what 'algorithms to run (in our case Pythia and Atlfast)
• Define the Pythia settings
• Define output parameters/ntuples

Create a file called joboptions_HiggsGeneration.py. You can download the file from: joboptions_HiggsGeneration.py.

c) Get additional steering files

There are some requires input files that you have to get. The way to obbtain them is using the command get_files.

get_files PDGTABLE.MeV

get_files PartPropSvc.py

get_files AtlfastStandardOptions.py

d) Run Athena

Running Athena is now a single line: athena.py -bs joboptions_HiggsGeneration.py

Note: The "-bs" flag is optional and tells athena to print out all commands it is processing:

e) Check the output

In the directory now an output file called HiggsNtuple.root has been produced. When you look in the file you'll find the Tree for the CBNT (MC Truth) and that for AtlFast (Event in ATLAS). Now you only have to write a ROOT macro to read the file and do your analysis.

Finished!

2. producing 10,000 events in 10 sets of 1000

When using the joboptions file in the example above you have produced 10 events, but when you want to have a larger production you want to automatise everything a bit:

Create a new joboption file for each job each having

• A unique random number seed for Pythia
• A user defined number of events
• An output ntuple that is different for each event
• Store output and Logfiles in a separate directory

To do just this a small script has been created.

a) Create a BASICS-directory

Create a directory with the basic information you require.

  
 cd MyGeneration/
 mkdir HiggsGen_BASICS
 cp PDGTABLE.MeV               ./HiggsGen_BASICS/
 cp PartPropSvc.py             ./HiggsGen_BASICS/
 cp AtlfastStandardOptions.py  ./HiggsGen_BASICS/
 

We also copy the joboptions file there and rename it

   
  cp joboptions_HiggsGeneration.py ./HiggsGen_BASICS/joboptions_HiggsGeneration.py.BASIC
  

b) Edit the standard joboptions file

  
 cd MyGeneration/HiggsGen_BASICS
 

To allow the script to change the job-dependent settings in the joboptions file we'll now have to change 3 lines in the joboptions file: joboptions_HiggsGeneration.py.BASIC.

1) Change Number of events

theApp.EvtMax = 10 . changes to ->

theApp.EvtMax = XNEVENTSX

2) Change Random number seeds for Pythia

AtRndmGenSvc.Seeds = ["PYTHIA 5769791 690419913", "PYTHIA_INIT 690501 4106941"]. changes to ->

AtRndmGenSvc.Seeds = ["PYTHIA XRNDPYTHIA0X XRNDPYTHIA1X", "PYTHIA_INIT XRNDPYTHIA2X XRNDPYTHIA3X"]

3) Change Name output file (and output directory)

NTupleSvc.Output = [ "FILE1 DATAFILE='./HiggsNtuple.root' OPT='NEW'" ]. changes to ->

NTupleSvc.Output = [ "FILE1 DATAFILE='./XOutputDirCBNTX/HiggsNtuple.JobXJOBNUMBERX.root' OPT='NEW'"]

c) Create an output directory (Ntuples and Logfiles)

 To store the ntuples and Logfiles we create an output directory:
  
 cd MyGeneration/
 mkdir HiggsGen_OUTPUT
 mkdir HiggsGen_OUTPUT/InputAndLogfiles
 

d) Get the script and tailor it to your needs

First copy the main script to your running directory

  
 cd /project/atlas/users/<your_login_name>/MyGeneration/
 cp /user/ivov/Higgs_Tutorial_Files/ShipOff_HiggsGen.py .
 

The main user control flags that need to be edited are listed at the top of the script in the

routine: Get_InputParameters

  Nevents_joboptions  =     100   # number of events to be generated per job
  Njobs               =       2   # Number of jobs
  f_LogFile           =       0   # Write to screen or logfile

  steering_files_dir  = "/data/atlas/users/<your_login_name>/scratch/MyGeneration/HiggsGen_BASICS/"     # basic input files
  output_dir          = "/data/atlas/users/<your_login_name>/scratch/MyGeneration/HiggsGen_OUTPUT/"     # output directory

By default what will happen is that for job 1, a directory called Job1 is produced that contains the files from HiggsGen_OUTPUT/ and a unique joboptions file (50 events with a unique random number sequence for Pythia). In the

directory a link is put to the HiggsGen_BASICS/ directory. After the job is finished the Ntuple called HiggsNtuple.Job1.root is put in that directory. For job number 2 a similar thing happened.

e) The real thing (logfiles)

Now, once this is running, you might want to change 2 more things.

First, you should opt for the automatic logfile:

f_LogFile           =       1  # Logfile yes/no

Then you should remove the # from the line

#CleanUp_Job(i_file)

This will make that at the end of the job both the logfile and the joboptions file for this job will

be copied to the directory "HiggsGen_OUTPUT/InputAndLogfiles" and that the directory is removed.

Finally, chaning the Number of events to 1000 and the number of jobs to 10, you will produce 10,000 events with $H\rightarrow ZZ^{*}\rightarrow \mu ^{+}\mu ^{-}\mu ^{+}\mu ^{-}$.