Photon induced process with MadGraph and Herwig

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Given the ever-growing complexity of the Monte Carlo event generators, the authors of popular Monte Carlo and matrix element programs attending the Physics at TeV Colliders Workshop in Les Houches, France at May 2001, have agreed on a universal interface to transfer parton level event configurations from matrix element event generators to showering and hadronization event generators. The parton level event generation information that is embedded in a minimal XML-style structure is called the Les Houches files and distinguished by a ".lhe" extension. Herwig authors were among the founders of the Les Houches accord and Herwig fully supports the use of this interface.

At this stage of our tutorial, we will attempt to use Les Houches event files to generate an event in Herwig. We target the inclusive dijet production event at 7 TeV, using an LHE file from MadGraph5.

Please make a folder and copy the input and LHE files in it;

Input file:

LHE file:

Alternatively, you can simply use the following commands:

mkdir LesHouches

cd LesHouches

wget https://phab-files.hepforge.org/file/download/n5ycv7s67f47i7nk37fi/PHID-FILE-bzz3zr7ar5bniyuqmct5/LHC-LesHouches.in

wget https://phab-files.hepforge.org/file/download/ktmalsrogbl4ec52dynp/PHID-FILE-73dmncv2ytrteho6g3gn/LHC-dijet.lhe.gz

Now, you can run the event by:

Herwig read LHC-LesHouches.in

Herwig run LHC-LesHouches.run -N 10000

By looking at the input files, one finds out that it is using the ATLAS_2012_I1082936 Rivet analysis plugin to compare the results against the exiting experimental data. To create the corresponding plots, run:

rivet-mkhtml LHC-LesHouches.yoda

and find the plots in "rivet-plots" directory.

Obviously, 10000 iterations are not nearly enough to cancel-out the statistical fluctuations in the results. However, running this event with the minimum of the required iterations could be time-consuming. We have already run this event for 40 million iterations:

Yoda file:

you can compare your results with our's, using

wget https://phab-files.hepforge.org/file/download/2pmgnyn6r6exhihaqfos/PHID-FILE-nkq6rz3dpso2n7cronmz/LesHouches40M.yoda

rivet-mkhtml LHC-LesHouches.yoda:N10K LesHouches40M.yoda:N40M