The First run

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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 will find under {Herwigpath}/share/Herwig/ or here into that folder.

You can also download the input file via

wget  https://phab-files.hepforge.org/file/download/d3y555lituggiomcwatj/PHID-FILE-hirg3s3rz7xph4yuaij6/LEP.in

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.log

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 input file LEP.in file and include the following part

read snippets/Rivet.in
insert /Herwig/Analysis/Rivet:Analyses 0 ALEPH_1996_S3486095

right above the line 'saverun LEP EventGenerator'

Now we need to run Herwig again. The steps are the same as above 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

Before we go on have a look at the created histograms and try to roughly understand what is being measured.

Optional: You can also include more Rivet analyses. Just go to the rivet homepage and try to add some additional LEP
analyses (ALEPH_, OPAL_ )

Congratulations, you have now mastered the simplest workflow of event generation

Simulate events and then compare with data.