For the first run we are going to simulate simple LEP events with the default setup and look at the output files.
First create a folder where you put everything related to the Herwig tutorial
mkdir herwig-tutorial
and copy the input file LEP.in that you find under /src into that folder.
Then type the following commands in order to simulate 1000 LEP events:
Herwig read LEP.in
Herwig run LEP.run -N 1000
In the next step have a look at the file LEP.log that displays the first 10 events of that run. Each event is made up of individual steps that reflect the treatment of the event as it passes through the various stages of the generator (hard subprocess, parton shower, hadronization and decays). Try to make sense of the numbers displayed and try to find the individual steps in the event record (the LEP.log file).
You can display files with
less LEP.in
Since only looking at numbers is tedious and we cannot really learn something from the .log file we now try to compare the simulation with data.
For that purpose we need to modify the LEP.in file and include the following part
read snippets/Rivet.in
insert /Herwig/Analysis/Rivet:Analyses 0 ALEPH_1996_S3486095
before the line 'saverun LEP EventGenerator'
Now we need to run Herwig again. The steps as above are the same but now we should have created a
LEP.yoda
file. In order to plot the yoda file we use the following command
rivet-mkhtml LEP.yoda
this creates a folder rivet-plots that collects all the created histograms of the ALEPH analysis. You can display the analysis in your browser by typing
firefox rivet-plots/index.html
Now before we go on have a look at the created histograms and try to roughly understand what is being measured here.
Optional: You can also include more rivet analyses. Just go to the rivet homepage and try to add some additional LEP
analyses.
Congratulations, you have now mastered the simplest workflow of event generation
Simulate events and then compare with data.