Photon-induced process in Herwig

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Here we demonstrate an example of photon-induced events in Herwig.

To start, create a new work directory:

mkdir photon_induced
cd photon_induced

Next, download below input/config/analysis files in your work directory.

1. MadGraph configure script: this is a script for generating a sample of unweighted yy > ll events with MadGraph.

wget https://phab-files.hepforge.org/file/download/fmev7v6idvr75ggbdth3/PHID-FILE-i3aaqziv52hgqrsztjuo/MG_make.sh

2. MadGraph parameter and run cards: parameter space and run statistics for the MadGraph run.

wget https://phab-files.hepforge.org/file/download/xjefkopi6whfilhore3q/PHID-FILE-kfvne4b34gu6thn2syt5/run_card.dat

wget https://phab-files.hepforge.org/file/download/6ox3c6if7ekcawjw33am/PHID-FILE-ynhnj545mdxfbtqytoqn/param_card.dat

3. Rivet analysis and plot setup: Rivet analysis, to be run alongside the Herwig setup.

wget https://phab-files.hepforge.org/file/download/drv32ihccvchwfm6qrjx/PHID-FILE-74aubf5x2iktkajdepci/RivetAnalysis_yy.cc

wget https://phab-files.hepforge.org/file/download/mjsx7nxjbmu3curex3ew/PHID-FILE-p3xj34mwaixlritunlmp/RivetAnalysis_yy.plot

4. Herwig Input files: the main Herwig input file.

wget https://phab-files.hepforge.org/file/download/ccjmisiezgugnatpxbqf/PHID-FILE-66o5cobqy5u3fydkyr7u/LesHouches.in

Once the files are downloaded, please have a look at MG_make.sh. It can be run by:

chmod +x MG_make.sh
[sudo] ./MG_make.sh

Once it is done, you should be able to see a new directory named "yyll" that contains the requited unweighted sample in yyll/Events/run_01/unweighted_events.lhe.gz.

We are now set to sun Herwig using these samples. Run

Herwig read LesHouches.in

It should generate a run file called LesHouches.run. Now execute

Herwig run LesHouches.run -N 10000

The last part asks Herwig to run this simulation for 10000 events only. After this is done, you should be able to see several files generated in your work directory. This will generate a number of files in your work directory:

• LesHouches.log: contains the details of each produced event, for the first 10 events (can be changed to include any number of events). The details include incoming/outgoing/intermediate particles and their kinematics. This is useful information to check what is actually going on under the hood.
• LesHouches.out: Statistics for the event handler, including the number of valid events (subtracting vetoed/scrapped events) and a list of sub-process categories with their event count and cross-section.
• LesHouches.tex: A list of publications, relevant to your Herwig setup, which you should cite if you are making use of this specific simulation.
• LesHouches.yoda: Specific results, according to the Rivet analysis you called.